Bicycle sprocket

Abstract

Bicycle sprocket for engagement with a chain (2), having a central axis of rotation (X, Y), the bicycle sprocket comprising: a sprocket main body (30, 40, 50); a plurality of teeth (32, 42, 52) arranged along a circumferential direction on a radially outer side of the sprocket main body (30, 40, 50); and at least one switching area (34, 44, 54), wherein the plurality of teeth (32, 42, 52) includes at least one first tooth (32a) having a first maximum axial width (W1) for engagement with an outer connecting plate (2a) of the chain (2), and at least one second tooth (32b) having a second maximum axial width (W2) for engagement with an inner connecting plate (2b) of the chain (2), wherein the first maximum axial width (W1) is greater than the second maximum axial width (W2), and wherein the switching region (34, 44, 54) includes a concave part (38) which is arranged further inward in a radial direction than the projections of the plurality of teeth (32, 42, 52).

Description

CROSS REFERENCE TO RELATED APPLICATIONSThis application claims the benefit of priority to U.S. Provisional Application No. 61 / 824,568, filed May 17, 2013, and U.S. Non-Provisional Application No. 14 / 053,630, filed October 15, 2013. The entire disclosure of U.S. Provisional Application No. 61 / 824,568 and U.S. Non-Provisional Application No. 14 / 053,630 are hereby incorporated by reference herein.BackgroundField of the InventionThis invention relates generally to a bicycle sprocket comprising the bicycle sprocket.Background InformationBicycle sprockets are provided to both a crank assembly located at the center of a bicycle and a rear wheel, the rotation of the crank assembly is transmitted to the rear wheel through a chain that meshes with the sprockets. In a bicycle chain, an inner link plate and an outer link plate are alternately connected, therefore, the distances between the outer link plate and the teeth of the sprockets are larger than the distances between the inner link plate and the teeth of the sprockets when the teeth of the sprockets have the same thickness. In view of this, conventional sprockets (for example, description of U.S. Pat. No. 4,174,642 A) are known in which the axial width of the teeth (the tooth thickness) with respect to the rotational center axis direction of the sprocket is designed such that the axial width of the teeth that engage with the outer link plate is larger than the axial width of the teeth that engage with the inner link plate. A conventional sprocket has teeth that taper diametrically outward. Therefore, it is unlikely that the distances between the sprocket and the chain will decrease and that the chain will disengage from the teeth of the sprocket.A bicycle crank assembly includes a crank arm and a sprocket. Among such bicycle crank assemblies is a known embodiment in which a plurality of sprockets having different numbers of teeth are mounted on the crank arm. The sprockets are provided for shifting and the chain is moved by a derailleur between the two sprockets having a different number of counts to perform the shifting action.The German document DE 10 2012 023 819 A1 teaches, for example, an individual chain ring for a bicycle front crank arrangement for engaging in a drive chain. The single sprocket includes a plurality of teeth formed around a periphery of the sprocket, the plurality of teeth having an even number of teeth. The plurality of teeth includes a first group of teeth and a second group of teeth alternately disposed between the first group of teeth. The first tooth group and the second tooth group are the same in number. Each of the first and second groups of teeth includes an outer side and an inner side opposite to the outer side, and each tooth of the first group of teeth includes at least one protrusion on the outer side, and each tooth of the second group of teeth is formed without a first protrusion on the outer side and the inner side.German document DE 10 2008 060 501 A1 teaches a multiple sprocket arrangement for a bicycle with a sprocket with a larger diameter and a sprocket with a smaller diameter, wherein the sprocket with a larger diameter has at least one auxiliary guide portion for facilitating displacement of a bicycle chain from the sprocket with a smaller diameter to the sprocket with a larger diameter.United States Patent No. 5,085,621 discloses a multistage sprocket assembly for a bicycle, the assembly comprising a larger sprocket and a smaller sprocket mounted adjacent to each other; the larger sprocket having a concave portion defined in a side surface thereof opposite to the smaller sprocket, the concave portion being arranged along a trajectory of an intermediate plate portion of a drive chain shifting from the smaller sprocket to the larger sprocket, the intermediate plate portion being positioned forward in a driving rotational direction of the sprocket assembly relative to an engagement guide plate portion of the chain first engaging a tooth of the larger sprocket.Japanese document JP S56-42 489 U discloses a sprocket for bicycles, particularly a sprocket body and a plurality of circumferentially provided tooth bodies on the outer periphery of the sprocket body, for use in a bicycle crank or a rear wheel hub for bicycles.German document DE 10 2012 013 645 A1 discloses a chain guide roller for a rear derailleur of a derailleur of a bicycle for guiding a chain, comprising an annular roller body having a central opening for rotatable mounting about an axis of rotation of the chain guide roller; a toothing having a plurality of radially protruding teeth which are arranged on an outer circumferential surface of the roller body, wherein a tooth gap is arranged in each case between two teeth adjacent in the circumferential direction, wherein individual teeth have a predetermined tooth width matched to the chain in the region of a root circle of the toothing. To improve the guiding properties, it is provided that the chain guide roller has at least one guide section with a greater width than the tooth width of at least one of the adjacent teeth on at least one part of the tooth gaps in the region close to a tooth gap base and / or on at least one part of the teeth.US 4 174 642 A discloses a chain drive comprising a sprocket rotatable in a plane and having an even number of wide and narrow tapered teeth, and a flexible chain comprising successive links having alternately wide and narrow tooth engaging link openings, the tooth width and the width of the link openings being measured in a direction transverse to the plane of sprocket rotation.SummaryA sprocket having teeth having different axial widths with respect to the rotational center axis direction of the sprocket is constituted of a structure for preventing the chain from easily disengaging from the teeth of the sprocket. Therefore, the shifting action becomes complicated when a sprocket having teeth having different axial widths is used in a conventional crank assembly to move a chain between two sprockets, thereby also increasing wear on the chain. The problem is solved by the subject matter of claim 1.An object of the present invention is to make the shifting action easier in a sprocket having teeth having different axial widths, while additionally reducing wear in shifting the chain from a smaller to a larger sprocket in a bicycle crank assembly.This object is achieved by the subject matter of the main claim. Preferred embodiments are defined in the dependent claims.Other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the accompanying drawings, discloses a preferred embodiment of the present invention.Brief Description of the DrawingsReferring now to the accompanying drawings which form a part of this original disclosure: FIG. 1 is a front view of a bicycle crank assembly according to the first embodiment of the present invention; FIG. 2 is a front perspective view of the first sprocket; FIG. 3 is a rear view of the first sprocket; FIG. 4 is a partial rear perspective view of the first and second sprockets; FIG. 5 is a partial side view of the first sprocket, the second sprocket, or the third sprocket when viewed from the radial outside; FIG. 6 is a front perspective view of the second sprocket; FIG. 7 is a front view of the bicycle crank assembly according to the second embodiment of the present invention; and FIG. 8 is a plan view of the third sprocket.Detailed Description of EmbodimentsSelected embodiments will now be explained with reference to the drawings.In FIG. 1, a bicycle crank assembly (hereinafter, referring to a crank assembly) 10 according to the first embodiment of the present invention includes a crank arm 12, a first sprocket 14, and a second sprocket 16, which are bicycle sprockets according to an embodiment of the present invention. The first sprocket 14 and the second sprocket 16 are front sprockets that can engage with a chain 2. The second sprocket 16 has fewer teeth than the first sprocket 14. the chain 2 includes an outer link plate 2 aand an inner link plate 2 b.Crank armThe crank arm 12 is integrally and rotatably connected to a crank shaft 19 and a crank shaft, respectively. The crank arm 12 includes a sprocket attachment part 20 and an arm part 22 provided either integrally or separately from the sprocket attachment part 20.The sprocket attachment part 20 includes a plurality (e.g., four) of sprocket attachment arms 24 arranged at intervals in the circumferential direction. The circumferential intervals of the sprocket attachment arms 24 may be equal intervals, but may be unequal intervals. In the first embodiment, the sprocket attachment arms 24 are arranged at equal intervals and are inclined upstream progressively in the rotational direction R of the crank arm 12 with respect to the radial direction. The sprocket attachment arms 24 have first attachment parts 24 ato attach the first sprocket 14. The first attachment parts 24 aare formed at the distal ends of the sprocket attachment arms 24. The sprocket attachment arms 24 have second attachment parts 24 bto attach the second sprocket 16. The second attachment parts 24 bare formed more inward in the radial direction than the first attachment parts 24 a. The first attachment parts 24 aand the second attachment parts 24 bare configured of, for example, through holes or screw holes or the like through which nothing more passes. In the first embodiment, the first attachment parts 24 aare configured from through holes, and the second attachment parts 24 bare configured from screw holes through which nothing more passes. The first sprocket 14 is fixed to the first attachment parts 24 aby first fixing bolts 26. The second sprocket 16 is fixed to the second attachment parts 24 bby second fixing bolts 28 (see FIG. 4 ).The arm portion 22 is formed either integrally with or separately from the sprocket attachment portion 20. In the first embodiment, the arm part 22 is integrally formed with the sprocket attachment part 20. The arm part 22 has a pedal attachment part 22 ato which a pedal (not illustrated) can be mounted at the distal end, and has a connection hole 22 bto which the pedal crank shaft 19 is integrally and rotatably connected at the proximal end.First sprocketThe first sprocket 14 has a rotational center axis X, and includes a first sprocket main body 30, a plurality (e.g., 30 to 60) of teeth 32 arranged along the circumferential direction on the radially outer side of the first sprocket main body 20, and includes a first shifting portion 32 as illustrated in FIGS. 2 to 5. The first sprocket main body 30 is an example of a sprocket main body. The first shift range 34 is an example of a shift range. The term "shift range" in the present invention means either a range where the chain engages with the teeth of a large sprocket during an upshift action from a small sprocket to a large sprocket or a range where the chain disengages from the teeth of the large sprocket during a downshift action from the large sprocket to the small sprocket. The first sprocket main body 30 and the teeth 32 are made of metal and are integrally formed. The first sprocket main body 30 includes a plurality (e.g., four) of first fixing parts 30 athat are fixed to the first attachment parts 24 aof the sprocket attachment arms 24 and are arranged at intervals in the circumferential direction. In the first embodiment, the first fixing parts 30 aare configured as through holes and are disposed at positions facing the plurality of first attaching parts 24. The first sprocket 14 is fixed to the sprocket attachment parts 24 by first fixing bolts 26 and a nut member (not illustrated) threadedly engaged with the first fixing bolts 26.There are thirty-six of the teeth 32 in the first embodiment, for example. The teeth 32 include at least one first tooth 32 athat has a first maximum axial width W 1 (see FIG. 5 ) and includes at least one second tooth 32 bthat includes a second maximum axial width W 2. The first teeth 32 aare formed to be capable of engaging with an outer link plate 2 aof the chain 2. The second teeth 32 bare formed to be capable of engaging with an inner link plate 2 bof the chain 2. The first maximum axial width W 1 is greater than the second axial width W 2. The first maximum axial width W 1 of the first teeth 32 ais, according to an aspect not according to the invention, in a range of 2.5 mm or greater and of 5.4 mm or less, and more preferably in a range of 3.0 mm or greater and of 4.5 mm or less. Once the first maximum axial width W 1 of the first teeth 32 ais in such a range, the teeth 32 aare easily engaged with the outer link plate 2 awithout being engaged with the inner link plate 2 b. The second maximum axial width W 2 of the second teeth 32 bis, according to an aspect not according to the invention, in a range of 1.5 mm or greater and 2.3 mm or less. Once the second maximum axial width W 2 of the second teeth 32 bis in such a range, the second teeth 32 bhave the necessary rigidity and are easily engaged with the inner link plate 2 b.The first teeth 32a are formed in a + (plus) shape when viewed from the radial outside as shown in Figs. 2 to 5, in an aspect not according to the present invention. The second teeth 32 bare formed in a (minus) shape when viewed from the radial outer side according to an aspect not according to the present invention. The first teeth 32 aand the second teeth 32 bare tapered so as to gradually decrease in axial width toward the radially outer side. The first teeth 32 aand the second teeth 32 bare thereby more easily engaged with the outer link plate 2 aand the inner link plate 2 b. Among the plurality of first teeth 32 a, first teeth 32 a 1, and first teeth 32 a 2 which are shift teeth 32 cdescribed below, in an aspect not according to the present invention, T shapes are formed as illustrated in FIG. 2 when viewed from the radial outer side in the first embodiment. The first teeth 32 a 1 are shift teeth 32 cfor downshifting wherein the chain 2 moves from the first sprocket 14 to the second sprocket 16, and the first teeth 32 a 2 are shift teeth 32 cfor upshifting wherein the chain 2 moves from the second sprocket 16 to the first sprocket 14. In the first embodiment, the first maximum axial width of the T-shaped first teeth 32 a 1, 32 a 2 is smaller than the first maximum axial width W 1 of the +-shaped first teeth 32 aand larger than the second maximum axial width W 2 of the --shaped second teeth 32 b.At least some of the first teeth 32 aand the second teeth 32 bare arranged alternately in the circumferential direction, i.e., adjacent to each other, and in the first embodiment, all of these teeth are arranged in this manner as shown in FIG. 2.The first shift range 34 includes, in an aspect not according to the present invention, the first shift teeth 32 cprovided on at least one of the teeth 32. The first ratchet teeth 32 care an example of ratchet teeth. In this embodiment, a plurality (e.g., four) of the first ratchet teeth 32 care provided. The first shift teeth 32 care provided between the connected first teeth 32 a 1 and the second teeth 32 b. The first shifting portion 34 includes a first protrusion 36 aand a second protrusion 36 bformed to be capable of supporting the chain 2. The first protrusion 36 aand the second protrusion 36 bare examples of protrusions. In addition, the first switching portion 34 includes a concave part 38 and a concave part 38 which are disposed further diametrically inside than the protrusions of the teeth 32.The first sprocket teeth 32 chave first guide surfaces 32 dfor guiding the chain 2 in a first surface 14 a(see FIG. 2 ) and a second surface 14 b(see FIG. 3 ) of the first sprocket 14 (as shown in FIGS. 2 and 3 ). The first guide surfaces 32 dare an example of a guide surface. The first guide surface 14 aof the first sprocket 14 is the front surface that is disposed on the axially outer side farther from the bicycle frame when the crank assembly 10 is mounted on the bicycle. The second surface 14 bis the rear surface disposed on the axially inner side closer to the bicycle frame. The first guide surfaces 32 dare recessed so as to gradually decrease in thickness toward the sides of the first shift teeth 32 c.The first protrusion 36 ais provided protrudingly in the second surface 14 bof the first sprocket main body 30 to guide the chain 2 to the teeth 32 of the first sprocket 14. The second protrusion 36 bis provided protrudingly in the second surface 14 bof the first sprocket main body 30 to guide the chain 2 to the first protrusion 36 a. In the first embodiment, the first protrusion 36 aand the second protrusion 36 bare provided as a pair (a plurality) spaced at intervals in the circumferential direction. The first protrusion 36 guides the chain to the second teeth 32 b, which are shown by hatching in FIG. 3 and which are upstream of the first protrusion 36 ain the progressive direction of rotation R of the crank assembly 10.The distance L 1 between the first protrusion 36 aand the second protrusion 36 bis larger than the longitudinal length L 2 of the outer link plate 2 aand / or the inner link plate 2 bof the chain 2, as shown in FIG. 1. The distance L 1 between the first protrusion 36 aand the second protrusion 36 bmay also be either equal to the longitudinal length L 2 of the outer link plate 2 aand / or to the inner link plate 2 bof the chain 2, or less than the longitudinal length L 2. The first protrusion 36 aand the second protrusion 36 bare securely molded to the first sprocket 14 by plastic deformation. In the present embodiment, the first protrusion 36 ais larger in diameter than the second protrusion 36 b.The concave part 38 is formed to make the chain 2 lighter in weight and supported in the first protrusion 36 ato be engaged with the teeth of the first sprocket 14, as shown in FIGS. 3 and 4. Therefore, the concave portion 38 is disposed in the vicinity of the first protrusion 36 aand further diametrically (radially) inward than the protrusions of the teeth 32. In the first embodiment, the concave part is disposed downstream of the first protrusion 36 ain the advancing rotational direction R and recessed in a substantially triangular shape inclined downstream (clockwise in FIG. 3 ) from the inner side of the diameter to the outer side. The chain 2 is thereby radially supported on the first protrusion 36 a.Second sprocketThe second sprocket 16 has a rotational center axis Y, and includes a second sprocket main body 40 and a plurality (e.g., 20 to 40) of teeth 42 arranged along the circumferential direction on the radially outer sides of the second sprocket main body 40, as shown in FIGS. 4 and 6. The second sprocket main body 40 is an example of a sprocket main body. The second shift range 44 is an example of a shift range. The second sprocket main body 40 and the teeth 42 are made of metal and integrally formed. The second sprocket main body 40 includes a plurality (e.g., four) of second fixing parts 40 athat are fixed to the second attachment parts 24 b(see FIG. 1 ) of the sprocket attachment arms 24 and are arranged at intervals in the circumferential direction. The second fixing parts 40 aare formed of through holes and are arranged at positions facing the plurality of second attaching parts 24 b. The second sprocket 16 is fixed to the sprocket attachment arms 24 by the second fixing bolts 28 (see FIG. 4 ) threadedly engaged with the second attachment part 24 b.The teeth 42 include at least one third tooth 42 ahaving a third maximum axial width W 3 (see FIG. 5 ) and includes at least one fourth tooth 42 bhaving a fourth maximum axial width W 4. The third teeth 42 aare formed to be capable of engaging with the outer link plate 2 aof the chain 2. The fourth teeth 42 bare formed to be capable of engaging with the inner link plate 2 bof the chain 2. The third maximum axial width W 3 is greater than the fourth maximum axial width W 4. The third maximum axial width W 3 of the third teeth 42 a,in an aspect not according to the invention, is in a range of 2.5 mm or greater and 5.4 mm or less, and more preferably in a range of 3.0 mm or greater and 4.5 mm or less. Once the third maximum axial width W 3 of the third teeth 42 ais in such a range, the third teeth 42 aare easily engaged with the outer link plate 2 awithout being engaged with the inner link plate 2 b. The fourth maximum axial width W 4 of the fourth teeth 42 bis in a range of 1.5 mm or greater and 2.3 mm or less, according to an aspect not according to the invention. Once the fourth maximum axial width W 4 of the fourth teeth 42 bis in such a range, the fourth teeth 42 bhave the necessary rigidity and are easily engaged with the inner link plate 2 b.The third teeth 42 aare formed in a + (plus) shape when viewed from the radially outer side, as shown in FIGS. 4, 5, and 6. The third teeth 42 aand the fourth teeth 42 bare tapered so as to gradually decrease in axial width toward the radially outer side. The third teeth 42 aand the fourth teeth 42 bare thus more easily engaged with the outer link plate 2 aand the inner link plate 2 b.At least some of the third teeth 42 aand the fourth teeth 42 bare arranged alternately in the circumferential direction, i.e., adjacent to each other, and in the first embodiment, all of these teeth are arranged in this manner as shown in FIG. 6.The second shift range 44 includes, according to an aspect not according to the present invention, the second shift teeth 42 cprovided on at least one of the teeth 42. The second ratchet teeth 42 care an example of ratchet teeth. In the first embodiment, a plurality (e.g., two) of second ratchet teeth 42 care provided. The second shift teeth 42 care provided at intervals in the circumferential direction. The second shift teeth 42 chave second guide surfaces 42 dfor guiding the chain 2 in a first surface 16 a(see FIG. 6 ) and a second surface 16 b(see FIG. 4 ) of the second sprocket 16 as shown in FIGS. 4 and 6. The second guide surfaces 42 dare an example of a guide surface. The first surface 16 aof the second sprocket 16 is the front surface disposed on the axially outer side farther away from the bicycle frame when the crank assembly 10 is mounted on the bicycle, and the second surface 16 bis the rear surface disposed on the axially inner side closer to the bicycle frame. The second guide surfaces 42 dare recessed to gradually decrease in thickness toward the sides of the second shift teeth 42 c.In the first embodiment, the second switching portion 44 may include the protrusions or the concave part of the first switching portion 34. However, the second switching portion may include only the protrusions or only the concave portion.Switching Action in the Crank ArrangementIn the bicycle crank assembly 10 having such a configuration, the bicycle crank assembly 10 is rotated in the advancing rotational direction R when the upshifting action from the second sprocket 16 to the first sprocket 14 is performed by a front derailleur (not illustrated). In this state, when the front derailleur moves from a position facing the second sprocket 16 to a position facing the first sprocket 14, the chain 2 disengages from the teeth of the second sprocket 16. At this time, the chain 2 is guided to the first protrusion 36a by the concave part 38 of the first shift range 34. Therefore, the chain 2 supported on the second protrusion 36 bis easily supported on the first protrusion 36 a.Once a downshifting operation from the first sprocket 14 to the second sprocket 16 is performed by the front derailleur (not shown), the bicycle crank assembly 10 is rotated in the advancing rotational direction R. In this state, when the front derailleur moves from a first position facing the first sprocket 14 to a position facing the second sprocket 16, the chain 2 disengages from the teeth of the first sprocket 14.Second EmbodimentIn the first embodiment, the bicycle crank assembly 10 has a first sprocket 14 and a second sprocket 16, but the crank assembly 110 of the second embodiment includes a third sprocket 18 in addition to the first sprocket 14 and the second sprocket 16 as shown in FIG. 7. The third sprocket 18 has fewer teeth than the second sprocket 16. The first sprocket 14 and the second sprocket 16 have the same configuration as in the first embodiment, and are denoted by the same symbols in FIG. 7 and are not described further.Third sprocketThe third sprocket 18 has a rotational center axis Z, and includes a third sprocket main body 50, a plurality (e.g., twenty to thirty) of teeth 52 arranged along the circumferential direction on the radially outer side of the third sprocket main body 50, and a third shift portion 54 as illustrated in FIG. 8. The third sprocket main body 50 is an example of a sprocket main body. The third shift range 54 is an example of a shift range. The third sprocket main body 50 and the teeth 52 are made of metal and are integrally formed. The third sprocket main body 50 includes a plurality (e.g., four) of third fixing parts 50 athat are fixed to the second attachment parts 24 b(see FIG. 1 ) of the sprocket attachment arms 24 and are arranged at intervals in the circumferential direction. The third fixing parts 50 aare formed of through holes and are arranged at positions facing the plurality of second attaching parts 24 b. The third sprocket 18, together with the second sprocket 16, is fixed to the sprocket attachment arms 24 by the second fixing bolts 28 (see FIG. 4 ) threadedly engaged with the second attachment parts 24 b.The teeth 52 include at least one fifth tooth 52 ahaving a fifth maximum axial width W 5 (see FIG. 5 ) and includes at least one sixth tooth 52 bhaving a sixth maximum width W 6. The fifth teeth 52 aare formed to be capable of engaging with the outer link plate 2 aof the chain 2. The sixth teeth 52 bare formed to be capable of engaging with the inner link plate 2 bof the chain 2. The fifth maximum axial width W 5 is greater than the sixth maximum axial width W 6. The fifth maximum axial width W 5 of the fifth teeth 52 ais, in an aspect not according to the invention, in a range of 2.5 mm or greater and 5.4 mm or less, and is in a range of 3.0 mm or greater and 4.5 mm or less. Once the fifth maximum axial width W 5 of the fifth teeth 52 is in such a range, the fifth teeth 52 aare easily engaged with the outer link plate 2 awithout being engaged with the inner link plate 2 b. The sixth maximum axial width W 6 of the sixth teeth 52 bis in a range of 1.5 mm or greater and 2.3 mm or less, according to an aspect not according to the invention. Once the sixth maximum axial width W 6 of the sixth teeth 52 bis in such a range, the sixth teeth 52 bhave the necessary rigidity and are easily engaged with the inner link plate 2 b.The fifth teeth 52 aare formed in a + (plus) shape when viewed from the radial outside as shown in FIGS. 5 and 8. The sixth teeth 52 bare formed in a - (minus) shape when viewed from the radial outside. The fifth teeth 52 aand the sixth teeth 52 bare tapered so as to gradually decrease in axial width toward the radially outer sides. The fifth teeth 52 aand the sixth teeth 52 bare thus more easily engaged with the outer link plate 2 aand the inner link plate 2 b.At least some of the fifth teeth 52 aand the sixth teeth 52 bare arranged alternately in the circumferential direction, i.e., adjacent to each other, and in the first embodiment, all of these teeth are arranged in this manner as shown in FIG. 8.The third shift range 54 includes, according to a non-inventive aspect, third shift teeth 52 cprovided on at least one of the teeth 52. In the second embodiment, a plurality (e.g., two) of third ratchet teeth 52 care provided. The third shift teeth 52 care provided at intervals in the circumferential direction. The third sprocket teeth 52 chave third guide surfaces 52 dfor guiding the chain 2 in a first surface 18 a(see FIG. 8 ) and a second surface (not shown) of the third sprocket 18 as shown in FIG. 8. The third guide surfaces 52 dare examples of a guide surface. The first surface 18 aof the third sprocket 18 is the front surface disposed on the axially outer side farther away from the bicycle frame when the crank assembly 10 is mounted on the bicycle, and the second surface is the rear surface disposed on the axially inner side closer to the bicycle frame. The third guide surfaces 52 dare recessed to gradually decrease in thickness toward the sides of the third ratchet teeth 52 c.In the third embodiment, the third switching portion 54 may include the protrusions or the concave part of the first switching portion 34. However, the third switching portion may include only the protrusions or only the concave portion.Further EmbodimentsEmbodiments of the present invention are described above. However, the present invention is not limited to these embodiments. Various deviations may be made within a range which does not depart from the scope of the invention. In particular, the plurality of embodiments and modifications disclosed in the specification may be combined as needed.(a) The first and second embodiments provide a front sprocket as an example of a bicycle sprocket. The present invention can also be applied to a rear sprocket(b) In the bicycle sprocket assembly of the first and second embodiments, first teeth and second teeth having different axial widths are provided to all of the sprockets. Any sprocket (e.g., the second and / or third sprockets, small in diameter) may be configured from the second teeth alone.(c) In the first and second embodiments, the first teeth according to an aspect of the present invention are formed in a + shape or a T shape when viewed from the radially outer side. These teeth may also be formed into other shapes such as diamond shape, trapezoidal shape, triangular shape or hexagonal shape.(d) In the first and second embodiments, the first switching portion 34 includes the second protrusion 36 b, but a second protrusion 36 bmay not be provided.(e) In the first and second embodiments, there are four sprocket attachment arms 24 a, but the number of sprocket attachment arms is not limited to 4.(f) In the first and second embodiments, the sprocket main bodies and the plurality of teeth are integrally formed. The sprocket main bodies and the plurality of teeth may also be formed separately from each other. The plurality of teeth may be made of, for example, metal, and the sprocket main bodies may be made of a synthetic resin such as carbon fiber reinforced resin or a metal different from teeth (for example, a lightweight metal such as aluminum) to reduce the weight.(g) The gear shift range of the sprockets may include the -(minus)-shaped second teeth 32 b, fourth teeth 42 b, and sixth teeth 52 b.It is also understood that although the terms "first" and "second" as used herein to describe different components should not be limited to these terms. These terms are used herein to distinguish one component from another only: thus, for example, a first component could be referred to as a second component and vice versa without departing from the teachings of the present invention.

Claims

A bicycle sprocket for engaging a chain (2) having a rotational center axis (X, Y), the bicycle sprocket comprising: a sprocket main body (30, 40, 50); a plurality of teeth (32, 42, 52) disposed along a circumferential direction on a radially outer side of the sprocket main body (30, 40, 50); and at least one shift range (34, 44, 54), wherein the plurality of teeth (32, 42, 52) includes at least one first tooth (32a) having a first maximum axial width (W1) for engaging with an outer link plate (2a) of the chain (2) and at least one second tooth (32b) having a second maximum axial width (W2) for engaging with an inner link plate (2b) of the chain (2), wherein the first maximum axial width (W1) is larger than the second maximum axial width (W2), and wherein the shift range (34, 44, 54) includes a concave part (38) disposed further inward in a radial direction than the shoulders of the plurality of teeth (32, 42, 52).The bicycle sprocket according to claim 1, wherein the plurality of teeth (32, 42, 52) includes a plurality of first teeth (32a1, 32a2) and / or a plurality of second teeth (32b).The bicycle sprocket according to claim 1 or 2, wherein at least some of the first and second teeth (32a, 32b) are alternately arranged in the circumferential direction.The bicycle sprocket according to any one of claims 1 to 3, wherein the first teeth (32a) and the second teeth (32b) are disposed adjacent to each other.The bicycle sprocket according to any one of claims 1 to 4, wherein the shift range (34, 44, 54) includes at least one protrusion (36a, 36b) configured to support the chain (2), in particular, the at least one protrusion (36a, 36b) includes a first protrusion (36a) and a second protrusion (36b) configured to support the chain (2).The bicycle sprocket according to claim 5, wherein a distance between the first protrusion (36a) and the second protrusion (36b) is longer than a longitudinal length of at least one of the outer link plate (2a) and the inner link plate (2b) of the chain (2).The bicycle sprocket according to claim 5, wherein a distance between the first protrusion (36a) and the second protrusion (36b) is either equal to or shorter than a longitudinal length of at least one of the outer link plate (2a) and the inner link plate (2b) of the chain (2).The bicycle sprocket according to any one of claims 1 to 7, wherein the at least one shift range (34, 44, 54) includes at least one pair of shift ranges (34, 44, 54), in particular a plurality of shift ranges (34, 44, 54).The bicycle sprocket according to any one of claims 1 to 8, wherein the bicycle sprocket is a front sprocket.

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