TWI894153B - Bicycle drive system and bicycle front sprocket assembly - Google Patents

Abstract

[Question] To provide a bicycle drive system and a front sprocket assembly for a bicycle that enable smooth shifting of gear ratios over a wide range. [Solution] A drive system comprises a crank assembly and a multiple rear sprocket assembly including a plurality of rear sprockets. The crank assembly includes a front sprocket, a crank arm, and a sprocket gear shifting mechanism that allows the sprocket gears of the front sprocket to be shifted relative to the crank arm at least in the axial direction of the front sprocket's rotational center axis. The plurality of rear sprockets include: a smallest rear sprocket, a largest rear sprocket, and at least 12 intermediate rear sprockets disposed between the two sprockets; an axial length is defined as a length between an axially outer surface of the smallest rear sprocket and an axially inner surface of the largest rear sprocket, and the axial length is greater than or equal to 47.5 mm.

Description

Bicycle drive system and bicycle front sprocket assembly

The present invention relates to a bicycle drive system and a bicycle front sprocket assembly.

Patent Document 1 discloses a bicycle drive system. The bicycle drive system includes a crank, a sprocket, and a sliding mechanism. The sliding mechanism connects the crank and sprocket so that they can slide in the axial direction of the sprocket's rotational center axis.

[Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2016-196236

A bicycle drive system and a bicycle front sprocket assembly are proposed that enable smooth changes in gear ratios over a wide range.

The first type of drive system of the present invention comprises: a crank assembly and a composite rear sprocket assembly including a plurality of rear sprockets; the crank assembly comprises: a front sprocket, a crank arm, and a sprocket gear shifting mechanism that allows the sprocket gears of the front sprocket to be shifted relative to the crank arm at least in the axial direction of the rotation center axis of the front sprocket; the plurality of rear sprockets comprises: a smallest rear sprocket, a largest rear sprocket, and a plurality of rear sprockets in the axial direction. At least 12 intermediate rear sprockets are disposed between the smallest rear sprocket and the largest rear sprocket; each of the plurality of rear sprockets has an axially outer surface and an axially inner surface relative to the rotational axis; the length in the axial direction between the axially outer surface of the smallest rear sprocket and the axially inner surface of the largest rear sprocket is defined as an axial length, and the axial length is not less than 47.5 mm.

The first type of bicycle drive system utilizes a sprocket gear shifting mechanism to create multiple rear sprocket assemblies with multiple stages, preventing chain slippage and improving drive efficiency. This allows for smooth gear ratio changes across a wide range.

According to the second type of drive system of the first type, the axial length is greater than 48 mm.

The second type of bicycle drive system suppresses chain slippage even when using a compound rear sprocket assembly with a wide range of gear ratios, achieving excellent drive efficiency.

According to the third type of drive system of the second type, the axial length is greater than 49 mm.

The Type 3 bicycle drive system suppresses chain dropout and provides excellent drive efficiency, even with a wide range of gear ratios in the compound rear sprocket assembly.

According to the fourth type of drive system of any one of the first to third types, the ratio of the total number of teeth of the largest rear sprocket to the total number of teeth of the smallest rear sprocket is 3.4 or greater.

The Type 4 bicycle drive system suppresses chain slippage even with a wide range of gear ratios in a compound rear sprocket assembly, achieving excellent drive efficiency.

In the fifth drive system according to any one of the first to fourth aspects, the sprocket density is defined as the value obtained by dividing the total number of the plurality of rear sprockets by the axial length, and the sprocket density is 0.28 or greater.

The Type 5 bicycle drive system suppresses chain slippage even with a wide range of gear ratios in a multiple rear sprocket assembly, achieving excellent drive efficiency.

According to the sixth aspect of the drive system of any one of aspects 1 to 5 above, the number of teeth of the smallest rear sprocket is 12 or less, and the number of teeth of the largest rear sprocket is 42 or more.

The sixth type of bicycle drive system suppresses chain slippage even with a wide range of gear ratios in a multiple rear sprocket assembly, achieving excellent drive efficiency.

According to the seventh aspect of the drive system of any one of aspects 1 to 6 above, the total number of the plurality of rear sprockets is 14 or more.

The seventh type of bicycle drive system suppresses chain slippage, even with a wide range of gear ratios in the compound rear sprocket assembly, achieving excellent drive efficiency.

According to the eighth aspect of the drive system of any one of aspects 1 to 7 above, the front sprocket is a single front sprocket.

The Type 8 bicycle drive system allows the front derailleur to be omitted from the bicycle drive system. This reduces the weight of the bicycle drive system and allows the rider to focus on rear shifting.

According to the ninth aspect of the drive system of any one of aspects 1 to 8, the sprocket gear shifting mechanism causes the front sprocket to shift relative to the crank arm in a total axis direction within a range of 5 mm to 30 mm.

The ninth type of bicycle drive system can effectively reduce the tilt angle of the bicycle chain between the front and rear sprockets relative to the center plane of the bicycle when the bicycle drive system is mounted on various frames.

According to a tenth aspect of the drive system according to any one of aspects 1 to 9, when the bicycle drive system is mounted on a bicycle and the front sprocket is positioned at the axial center point of the total axial displacement width of the front sprocket relative to the crank arm caused by the sprocket gear shifting mechanism, at least five of the intermediate rear sprockets are arranged in the axial direction between the axial center plane of the largest rear sprocket and the front sprocket.

The tenth type bicycle drive system can reduce the inclination angle of the bicycle chain relative to the center plane of the bicycle when the bicycle chain is engaged with the smallest rear sprocket of the multiple rear sprocket assembly.

The eleventh embodiment of the present invention is a front sprocket assembly for a bicycle, comprising: a front sprocket and a sprocket gear shifting mechanism; the front sprocket comprises: a sprocket body and a plurality of sprocket gears arranged on the periphery of the sprocket body; the sprocket body comprises: a first connecting portion having a first fastening axis, a second connecting portion having a second fastening axis, a third connecting portion having a third fastening axis, and a fourth connecting portion having a fourth fastening axis; the sprocket gear shifting mechanism comprises: a sprocket carrier and a base member; the sprocket carrier is coupled to the front sprocket; the base member , coupled to one of the crank arm and the crank axle; the sprocket gear shifting mechanism, when the bicycle front sprocket assembly is assembled to the crank axle and the crank arm, allows the plurality of sprocket gears of the front sprocket to be shifted relative to the crank arm and the crank axle in the axial direction of at least the rotation center axis of the front sprocket; the sprocket carrier can move relative to the base member, and the sprocket carrier includes: a fifth connecting portion having a fifth fastening axis, a sixth connecting portion having a sixth fastening axis, a seventh connecting portion having a seventh fastening axis part, and an 8th connecting part having an 8th fastening axis; the 2nd connecting part is separated from the 1st connecting part in the circumferential direction of the rotation center axis of the front sprocket and there is no other connecting part between them; the 3rd connecting part is separated from the 2nd connecting part in the circumferential direction and there is no other connecting part between them; the 4th connecting part is separated from the 1st connecting part and the 3rd connecting part in the circumferential direction and there is no other connecting part between them, and in the assembled state, the crank arm is located between the 1st connecting part and the 4th connecting part in the circumferential direction; the 6th connecting part is separated from the 2nd connecting part in the circumferential direction and there is no other connecting part between them. The connecting portion is spaced apart from the fifth connecting portion in the circumferential direction and has no other connecting portion therebetween; the seventh connecting portion is spaced apart from the sixth connecting portion in the circumferential direction and has no other connecting portion therebetween; the eighth connecting portion is spaced apart from the fifth and seventh connecting portions in the circumferential direction and has no other connecting portion therebetween, and in the assembled state, the crank arm is positioned between the fifth and eighth connecting portions in the circumferential direction; the first fastening axis of the first connecting portion and the fifth fastening axis of the fifth connecting portion are formed The first common axis is aligned with each other so that the first fastening member passes through at least one of the first connecting portion and the fifth connecting portion; the second fastening axis of the second connecting portion and the sixth fastening axis of the sixth connecting portion are aligned with each other on the second common axis so that the second fastening member passes through at least one of the second connecting portion and the sixth connecting portion; the third fastening axis of the third connecting portion and the seventh fastening axis of the seventh connecting portion are aligned with each other on the third common axis so that the third fastening member passes through the third connecting portion and the sixth connecting portion. at least one of the 7th connecting parts; the 4th fastening axis of the 4th connecting part and the 8th fastening axis of the 8th connecting part are made to be aligned with each other on the 4th common axis so that the 4th fastening member passes through at least one of the 4th connecting part and the 8th connecting part; the 1st connecting angle is used to make the other common axis not be located between the 1st common axis and the 2nd common axis in the circumferential direction, and is defined as the 1st reference line extending from the rotation center axis toward the 1st common axis in the circumferential direction and the 1st reference line extending from the rotation center axis toward the 1st common axis in the circumferential direction. The second connecting angle is defined as the angle between the second reference line extending from the second common axis and the third common axis in the circumferential direction so that the other common axis is not located between the second common axis and the third common axis. The second connecting angle is defined as the angle between the second reference line and the third reference line extending from the rotation center axis toward the third common axis in the circumferential direction so that the other common axis is not located between the third common axis and the fourth common axis in the circumferential direction. The angle between fourth reference lines extending toward the fourth common axis; a fourth connection angle, defined as the angle between the fourth reference line and the first reference line in the circumferential direction, is used to ensure that other common axes are not located between the fourth common axis and the first common axis in the circumferential direction; at least one of the first connection angle, the second connection angle, the third connection angle, and the fourth connection angle is different from another one of the first connection angle, the second connection angle, the third connection angle, and the fourth connection angle.

The 11th type of bicycle front sprocket assembly efficiently transmits the force applied to the crankarms during pedaling to the bicycle chain, improving driving efficiency.

According to the 11th and 12th aspects of the bicycle front sprocket assembly of the present invention, the first connection angle is smaller than the second connection angle and the fourth connection angle.

The 12th type of bicycle front sprocket assembly can improve driving efficiency.

In the 11th, 12th, or 13th aspect of the bicycle front sprocket assembly of the present invention, the third connection angle is smaller than the second connection angle and the fourth connection angle.

The 13th type of bicycle front sprocket assembly improves driving efficiency.

In a fourteenth aspect of the bicycle front sprocket assembly according to any one of the eleventh to thirteenth aspects, the first connection angle is equal to the third connection angle.

The 14th type of bicycle front sprocket assembly can improve driving efficiency.

In a fifteenth aspect of the bicycle front sprocket assembly according to any one of the eleventh to fourteenth aspects, the second connection angle is different from the fourth connection angle.

The bicycle front sprocket assembly of the fifteenth embodiment can optimize the rigidity of the front sprocket.

According to the 15th and 16th aspects of the bicycle front sprocket assembly of the present invention, the second connection angle is smaller than the fourth connection angle.

The sixteenth embodiment of the bicycle front sprocket assembly optimizes the rigidity of the front sprocket.

According to a seventeenth aspect of the bicycle front sprocket assembly according to any one of aspects 11 to 16, the front sprocket comprises: a first axial surface; and a second axial surface opposite the first axial surface in the axial direction; the second axial surface is opposed to the center plane of the bicycle when the bicycle front sprocket assembly is mounted on the bicycle; and the first to fourth common axes are arranged in order of the first to fourth common axes in the circumferential direction counterclockwise from the crank arm when viewed from the first axial surface toward the second axial surface in the axial direction.

The 17th type of bicycle front sprocket assembly improves driving efficiency.

In the bicycle front sprocket assembly according to the eighteenth aspect of any one of the eleventh to seventeenth aspects, the base member is detachably connected to one of the crank axle and the crank arm by spline engagement.

The eighteenth embodiment of the bicycle front sprocket assembly can improve the maintainability of the front sprocket.

The 19th embodiment of the present invention is a front sprocket assembly for a bicycle, comprising: a front sprocket and a sprocket gear shifting mechanism; the front sprocket comprises: a sprocket body and a plurality of sprocket gears arranged on the periphery of the sprocket body; the sprocket gear shifting mechanism comprises: a sprocket carrier and a base member; the sprocket carrier is coupled to the front sprocket; the base member is coupled to the crank arm and The sprocket gear shifting mechanism, when the bicycle front sprocket assembly is assembled to the crank axle and the crank arm, allows the plurality of sprocket gears of the front sprocket to be shifted relative to the crank arm and the crank axle in the axial direction of at least the rotation center axis of the front sprocket; the sprocket carrier can be relative to the base member The sprocket gear shifting mechanism includes: a first sliding portion having a first sliding center point, a second sliding portion having a second sliding center point, a third sliding portion having a third sliding center point, and a fourth sliding portion having a fourth sliding center point; the second sliding portion is spaced apart from the first sliding portion in a circumferential direction of the rotational axis of the front sprocket and has no other connection therebetween; the third sliding portion is spaced apart from the second sliding portion in the circumferential direction and has no other connection therebetween; the fourth sliding portion is spaced apart from the first sliding portion and the third sliding portion in the circumferential direction and has no other connection therebetween, so that the crank arm is positioned between the first sliding portion and the fourth sliding portion in the circumferential direction in the assembled state; the first sliding portion is spaced apart from the first sliding portion and the third sliding portion in the circumferential direction and has no other connection therebetween; The first sliding angle is used to prevent other sliding center points from being located between the first sliding center point and the second sliding center point in the circumferential direction, and is defined as the angle between the first sliding reference line extending from the rotation center axis toward the first sliding center point in the circumferential direction and the second sliding reference line extending from the rotation center axis toward the second sliding center point; the second sliding angle is used to prevent other sliding center points from being located between the second sliding center point and the third sliding center point in the circumferential direction, and is defined as the angle between the second sliding reference line and the third sliding reference line extending from the rotation center axis toward the third sliding center point in the circumferential direction; the third sliding angle is used to prevent other sliding center points from being located between the second sliding center point and the third sliding center point in the circumferential direction. The angle between the third sliding center point and the fourth sliding center point is defined as the angle between the third sliding reference line and a fourth sliding reference line extending from the rotational axis toward the fourth sliding center point in the circumferential direction. The fourth sliding angle is defined as the angle between the fourth sliding reference line and the first sliding reference line in the circumferential direction, so that other sliding center points are not located between the fourth sliding center point and the first sliding center point in the circumferential direction. At least one of the first sliding angle, the second sliding angle, the third sliding angle, and the fourth sliding angle is different from another of the first sliding angle, the second sliding angle, the third sliding angle, and the fourth sliding angle.

The 19th type of bicycle front sprocket assembly improves the rigidity of the sprocket gear shifting mechanism.

According to the 19th and 20th aspects of the bicycle front sprocket assembly of the present invention, the first sliding angle is smaller than the second sliding angle and the fourth sliding angle.

The 20th type of bicycle front sprocket assembly improves the rigidity of the sprocket gear shifting mechanism.

According to the 19th, 20th, or 21st aspect of the bicycle front sprocket assembly of the present invention, the third sliding angle is smaller than the second sliding angle and the fourth sliding angle.

The 21st type of bicycle front sprocket assembly improves the rigidity of the sprocket gear shifting mechanism.

In the bicycle front sprocket assembly according to the 22nd aspect of any one of the 19th to 21st aspects, the first sliding angle and the third sliding angle are equal.

The 22nd type of bicycle front sprocket assembly improves the rigidity of the sprocket gear shifting mechanism.

In the 23rd aspect of the bicycle front sprocket assembly according to any one of the 19th to 22nd aspects, the second sliding angle is different from the fourth sliding angle.

The 23rd type of bicycle front sprocket assembly improves the rigidity of the sprocket gear shifting mechanism.

In the 24th embodiment of the bicycle front sprocket assembly according to any one of the 19th to 23rd embodiments, the second sliding angle is smaller than the fourth sliding angle.

The 24th type of bicycle front sprocket assembly improves the rigidity of the sprocket gear shifting mechanism.

According to a 25th aspect of the bicycle front sprocket assembly according to any one of aspects 19 to 24, the front sprocket comprises: a first axial surface; and a second axial surface opposite to the first axial surface in the axial direction; the second axial surface is opposed to the center plane of the bicycle when the bicycle front sprocket assembly is mounted on the bicycle; and the first to fourth sliding center points are arranged in this order in the counterclockwise direction from the crank arm in the circumferential direction when viewed from the first axial surface toward the second axial surface in the axial direction.

The 25th type of bicycle front sprocket assembly improves the rigidity of the sprocket gear shifting mechanism.

In the bicycle front sprocket assembly according to the 26th aspect of any one of the 19th to 25th aspects, the base member is detachably connected to one of the crank axle and the crank arm by spline engagement.

The twenty-sixth embodiment of the bicycle front sprocket assembly can improve the maintainability of the front sprocket.

A twenty-seventh aspect of the present invention is a front sprocket assembly for a bicycle, comprising: a front sprocket and a sprocket gear shifting mechanism; the front sprocket comprises: a sprocket body and a plurality of sprocket gears disposed on the outer periphery of the sprocket body; the sprocket body comprises at least one connecting portion; the sprocket gear shifting mechanism comprises: a sprocket carrier and a base member; the sprocket carrier is coupled to the front sprocket; the base member is coupled to one of a crank arm and a crank axle; the sprocket gear shifting mechanism is assembled to the crank axle and the crank arm in the front sprocket assembly for a bicycle. When assembled, the assembly allows the plurality of sprocket teeth of the front sprocket to be displaced relative to at least one of the crank arm and the crank axle in the axial direction of the rotational center axis of the front sprocket; the sprocket carrier is movable relative to the base member; the sprocket carrier includes at least one additional connecting portion; the at least one connecting portion and the at least one additional connecting portion are coupled to each other via at least one fastening member; the sprocket tooth shifting mechanism includes at least one sliding portion; the total number of the at least one fastening member is equal to the total number of the at least one sliding portion.

With the twenty-seventh embodiment of the bicycle front sprocket assembly, the number of sliding portions between the sprocket carrier and the sprocket is equal to the number of sliding portions between the base member and the sprocket carrier, enabling efficient transmission of driving force from the crankshaft to the sprocket.

According to the 27th and 28th aspects of the bicycle front sprocket assembly of the present invention, the base member is detachably connected to one of the crank axle and the crank arm by spline engagement.

The bicycle front sprocket assembly according to the twenty-eighth embodiment can improve the maintainability of the front sprocket.

In the bicycle front sprocket assembly according to the twenty-seventh, twenty-eighth, or twenty-ninth aspect of the present invention, the at least one connecting portion comprises a plurality of connecting portions, the at least one additional connecting portion comprises a plurality of connecting portions, the at least one fastening member comprises a plurality of fastening members, and the at least one sliding portion comprises a plurality of sliding portions, and the total number of the plurality of fastening members is equal to the total number of the plurality of sliding portions.

The 29th type bicycle front sprocket assembly enables efficient transmission of driving force from the crankshaft to the sprocket.

In the 30th aspect of the bicycle front sprocket assembly according to any one of aspects 27 to 29 of the present invention, the at least one sliding portion is disposed near at least one fastening member in the assembled state.

The 30th model bicycle front sprocket assembly enables efficient transmission of driving force from the crankshaft to the sprocket.

In the 31st aspect of the bicycle front sprocket assembly according to any one of the 27th to 30th aspects of the present invention, the at least one sliding portion is disposed upstream in the driving rotational direction relative to the at least one fastening member in the assembled state.

The 31st type bicycle front sprocket assembly enables efficient transmission of driving force from the crankshaft to the sprocket.

A 32nd aspect of the present invention is a front sprocket assembly for a bicycle, comprising: a front sprocket and a sprocket gear shifting mechanism; the front sprocket comprising: a sprocket body; and a plurality of sprocket gears disposed on the periphery of the sprocket body in a circumferential direction of a rotational axis of the front sprocket; the plurality of sprocket gears comprising: at least one first tooth having a first maximum chain engagement axial width relative to the rotational axis; and at least one second tooth having a second maximum chain engagement axial width relative to the rotational axis; the first maximum chain engagement axial width being greater than 100 mm in the axial direction of the rotational axis. The second maximum chain engagement axial width; the sprocket gear shifting mechanism comprises: a sprocket carrier and a base member; the sprocket carrier is coupled to the front sprocket; the base member is coupled to one of the crank arm and the crank axle via a groove; the sprocket gear shifting mechanism, when the bicycle front sprocket assembly is assembled to the crank axle and the crank arm, allows the plurality of sprocket gears of the front sprocket to be shifted relative to one of the crank arm and the crank axle in an axial direction of at least the rotational center axis of the front sprocket; the sprocket carrier is movable relative to the base member.

The 32nd type bicycle front sprocket assembly, which includes a sprocket gear shifting mechanism, can improve driving efficiency and enhance the chain retention force of the front sprocket.

According to the 32nd and 33rd aspects of the bicycle front sprocket assembly of the present invention, the base member is detachably connected to one of the crank axle and the crank arm by spline engagement.

The thirty-third embodiment of the bicycle front sprocket assembly can improve the maintainability of the front sprocket.

The bicycle front sprocket assembly according to the 32nd, 33rd, or 34th aspect of the present invention further comprises a locking member, which is configured to inhibit displacement of the base member relative to one of the crank arm and the crank axle in the assembled state and engage with the one of the crank arm and the crank axle.

The 34th type bicycle front sprocket assembly allows for easy attachment and detachment of the front sprocket.

In the 35th aspect of the bicycle front sprocket assembly according to any one of aspects 32 to 34 of the present invention, the first maximum chain engagement axial width is greater than the inner link axial spacing defined between a pair of inner link plates of the axial bicycle chain, and less than the outer link axial spacing defined between a pair of outer link plates of the axial bicycle chain; and the second maximum chain engagement axial width is less than the inner link axial spacing.

The 35th type bicycle front sprocket assembly can enhance the chain retention force of the front sprocket.

In the 36th aspect of the bicycle front sprocket assembly according to any one of aspects 32 to 35 of the present invention, the first radial length is defined as the length between the first radial outermost end of the at least one first tooth and the rotational axis in a radial direction of the rotational axis; the second radial length is defined as the length between the second radial outermost end of the at least one second tooth relative to the rotational axis and the rotational axis; the first radial length is greater than the second radial length.

With the thirty-sixth embodiment of the bicycle front sprocket assembly, the first tooth having the first radial length engages earlier than the second tooth during rotation of the front sprocket. This ensures stable engagement of the bicycle chain and enhances the front sprocket's holding force on the bicycle chain.

According to the 35th and 37th aspects of the bicycle front sprocket assembly of the present invention, the first maximum chain engagement axial width of the at least one first tooth is at least 75% of the axial spacing of the outer link.

The 37th model bicycle front sprocket assembly can enhance the chain retention force of the front sprocket.

In the 38th aspect of the bicycle front sprocket assembly according to any one of the 32nd to 37th aspects of the present invention, the at least one first tooth has a first axial tooth end centerline offset in the axial direction from a first axial tooth bottom center plane of the at least one first tooth.

The 38th-instance bicycle front sprocket assembly can enhance the holding force of the bicycle chain when the tooth end of the bicycle chain is offset to the side near the first tooth relative to the center plane of the bicycle.

In the 39th aspect of the bicycle front sprocket assembly according to any one of aspects 32 to 37 of the present invention, the at least one second tooth has a second axial tooth end centerline offset in the axial direction from a second axial tooth bottom center plane of the at least one second tooth.

The 39th type bicycle front sprocket assembly can improve the holding force of the bicycle chain when the tooth end of the bicycle chain is offset to the side near the second tooth relative to the center plane of the bicycle.

In the 40th aspect of the bicycle front sprocket assembly according to any one of aspects 32 to 39 of the present invention, the at least one first tooth is asymmetrical in the circumferential direction relative to the centerline of the first circumferential tooth base.

The 40th model bicycle front sprocket assembly can enhance the chain retention force of the front sprocket.

In the 41st aspect of the bicycle front sprocket assembly according to any one of aspects 32 to 40 of the present invention, the at least one second tooth is asymmetrical in the circumferential direction relative to the centerline of the second circumferential tooth base.

The 41st type bicycle front sprocket assembly can enhance the chain retention force of the front sprocket.

In the 42nd aspect of the bicycle front sprocket assembly according to any one of the 32nd to 41st aspects of the present invention, the at least one first tooth is asymmetrical in the axial direction relative to the center plane of the tooth bottom in the first axial direction.

The 42nd type bicycle front sprocket assembly can enhance the chain retention force of the front sprocket.

In the 43rd aspect of the bicycle front sprocket assembly according to any one of aspects 32 to 42 of the present invention, the at least one second tooth is asymmetrical in the axial direction relative to the center plane of the tooth bottom in the second axial direction.

The 43rd type bicycle front sprocket assembly can enhance the chain retention force of the front sprocket.

In a 44th aspect of the bicycle front sprocket assembly according to any one of aspects 32 to 43 of the present invention, the at least one first tooth comprises a plurality of first teeth, the at least one second tooth comprises a plurality of second teeth, and the plurality of first teeth and the plurality of second teeth are alternately arranged in the circumferential direction.

The 44th type bicycle front sprocket assembly can enhance the chain retention force of the front sprocket.

The bicycle drive system of the present invention utilizes a sprocket gear shifting mechanism to create multiple stages of multiple rear sprocket assemblies, preventing chain slippage and improving drive efficiency. It also enables smooth gear ratio changes over a wide range.

A: Bicycle

AC1: 1st common axis

AC2: Second common axis

AC3: Third common axis

AC4: 4th common axis

AF1: First fixed axis

AF2: Second fixed axis

AF3: Third Fixing Axis

AF4: 4th fixed axis

AF5: Fifth fixed axis

AF6: 6th fixed axis

AF7: 7th fixed axis

AF8: 8th fixed axis

AG1: First connection angle

AG2: Second connection angle

AG3: 3rd connection angle

AG4: 4th connection angle

AGS1: 1st sliding angle

AGS2: Second sliding angle

AGS3: 3rd sliding angle

AGS4: 4th sliding angle

CA: Center of rotation axis

CS: Center plane

CST1: Center plane of tooth bottom in the first axial direction

CST2: Center plane of tooth bottom in the second axis direction

LA: axial length

LCRT1: Centerline of tooth end in the first axis direction

LCRT2: Centerline of tooth end in the second axis direction

LCT1: Centerline of tooth bottom in the first rotation direction

LCT2: Centerline of tooth bottom in the second rotation direction

LR1: Reference Line 1

LRS1: 1st radial length

LR2: Second reference line

LRS2: Second radial length

LR3: 3rd reference line

LR4: 4th reference line

PCR: Axial Center Point

PCS: Axial Center Plane

PRS1: 1st sliding reference line

PRS2: Second sliding reference line

PRS3: 3rd Sliding Reference Line

PRS4: 4th Sliding Reference Line

PS1: First sliding center point

PS2: Second sliding center point

PS3: 3rd sliding center point

PS4: 4th sliding center point

RD: Total axis displacement width

WA1: Width of the first largest chain clip in the axial direction

WA2: Second largest chain width in the axial direction

WAI: Inner connecting rod axial spacing

WAJ: Axial spacing of outer connecting rod

2: Crankshaft

4: Crank Arm

6: Front sprocket

8:Rear sprocket

10: Bicycle chain

12: Bicycle drive system

14: Crank assembly

16: Compound rear sprocket assembly

18: Sprocket gear

20: Sprocket gear shift mechanism

22: Smallest rear sprocket

24: Largest rear sprocket

26: Middle rear sprocket

30: Axial outer surface

32: Axial inner surface

34: Bicycle front sprocket assembly

36: Sprocket body

38: 1st axis direction surface

40: 2nd axis direction surface

42: Sprocket carrier

44: Base components

46: Locking mechanism

52: Sliding part

52A: 1st sliding part

52B: Second sliding part

52C: 3rd sliding part

52D: 4th sliding part

60: Connection

60E: 5th Link

60F: 6th Connection

60G: 7th Link

60H: 8th Connection

60X: Additional connection part

64: Fastening components

64A: First fastening member

64B: Second fastening member

64C: Third fastening member

64D: 4th fastening member

70A: First connection

70B: Second connection

70C: Third connection

70D: 4th connection

70X: Connection

82: 1st tooth

82a: 1st radial outermost tooth end

84: 2nd tooth

84a: The outermost tooth of the second radial direction

92: Inner connecting rod

94: External connecting rod

[Figure 1] is a schematic diagram of a bicycle including a bicycle drive system according to the first embodiment, viewed from above.

[Figure 2] is a schematic diagram showing an example of a front sprocket assembly for a bicycle, viewed from above.

[Figure 3] is a schematic diagram showing another example of a front sprocket assembly for a bicycle, viewed from above.

[Figure 4] is a top view of the multiple rear sprocket assembly.

[Figure 5 is a perspective view of a device including a bicycle front sprocket assembly according to the first to third embodiments.]

[Figure 6] is a side view of a device including a front sprocket assembly for a bicycle.

[Figure 7] is an exploded perspective view of a device including a bicycle front sprocket assembly.

[Figure 8] is an exploded perspective view of the sprocket gear shifting mechanism.

[Figure 9] is an exploded perspective view of the sliding portion and retaining member.

[Figure 10] is a cross-sectional view along line X-X in Figure 6.

[Figure 11] is an enlarged view of a portion of Figure 10.

[Figure 12] is a side view of the front sprocket.

[Figure 13] is a side view of the sprocket carrier.

Figure 14 is a side view of the front sprocket and sprocket carrier assembly.

Figure 15 is a side view of the front sprocket, sprocket gear shifting mechanism, and crank arm assembly.

Figure 16 is a cross-sectional view of the bicycle front sprocket assembly taken along line XVI-XVI in Figure 6.

Figure 17 is a side view of the bicycle front sprocket assembly according to the fourth embodiment.

Figure 18 is a partially enlarged view of the front sprocket of the fifth embodiment.

[Figure 19] is a top view of the first tooth.

[Figure 20] is a top view of the second tooth.

Figure 21 is a diagram showing the relationship between the first and second teeth of a bicycle chain.

[Figure 22] is a side view of the first tooth.

[Figure 23] is a side view of the second tooth.

<First Implementation Method>

Refer to Figure 1 for an explanation of the bicycle drive system 12.

Figure 1 is a top view of a human-powered vehicle equipped with a bicycle drive system 12, showing only the bicycle drive system 12. A human-powered vehicle refers to a vehicle that uses human power, at least in part, for propulsion, including vehicles that utilize electric power to assist human power. Human-powered vehicles do not include vehicles that utilize a power source other than human power. Human-powered vehicles do not include vehicles that are powered solely by an internal combustion engine. Typical human-powered vehicles are small and lightweight, and do not require a driver's license for public transportation. The human-powered vehicle shown includes bicycle A. Bicycle A includes mountain bikes and road bikes. Specifically, the human-powered vehicle is bicycle A. Bicycle A includes a frame 1 for supporting two wheels, a crankshaft 2 rotatably supported by frame 1, a pair of crank arms 4 disposed at either end of crankshaft 2, a front sprocket 6, a rear sprocket 8, and a bicycle chain 10. Bicycle A also includes a bicycle drive system 12.

The bicycle drive system 12 is described with reference to Figures 1 to 4.

As shown in FIG1 , the bicycle drive system 12 includes a crank assembly 14 and a multiple rear sprocket assembly 16 including a plurality of rear sprockets 8 .

The crank assembly 14 includes a front sprocket 6, a crank arm 4, and a sprocket gear shifting mechanism 20 that allows the sprocket gear 18 of the front sprocket 6 to shift relative to the crank arm 4 in at least the axial direction DA about the rotational axis CA of the front sprocket 6.

The plurality of rear sprockets 8 include a smallest rear sprocket 22, a largest rear sprocket 24, and at least twelve intermediate rear sprockets 26 arranged between the smallest rear sprocket 22 and the largest rear sprocket 24 in the axial direction DA.

The crank assembly 14 is mounted on the frame 1 of the bicycle A. The multiple rear sprocket assembly 16 is mounted on the hub of the rear wheel of the bicycle A. The bicycle chain 10 is wound around the front sprocket 6 and the multiple rear sprocket assembly 16.

In one example of the sprocket gear shifting mechanism 20 of the present invention shown in FIG. 2 , by shifting the front sprocket 6 in the axial direction DA about the rotational axis CA of the front sprocket 6, the sprocket gears 18 are displaced parallel to the axial direction DA of the rotational axis CA of the front sprocket 6. FIG. 2 shows, as a solid line, a first position P1 of the front sprocket 6 when the sprocket gear shifting mechanism 20 is positioned closest to the center plane CS of the bicycle A. FIG. 2 shows, as a two-point chain line, a second position P2 of the front sprocket 6 when the sprocket gear shifting mechanism 20 is positioned furthest from the center plane CS of the bicycle A. The distance between the first position P1 and the second position P2 is defined as the total axial displacement width RD of the front sprocket 6. The midpoint between the first position P1 and the second position P2 in the axial direction DA is defined as the axial center point PCR.

In another example of the sprocket gear shifting mechanism 20 of the present invention shown in FIG3 , by causing the front sprocket 6 to swing in a swing direction DZ centered on an axis CZ extending in the vertical direction of the human-powered bicycle, the sprocket gear 18 is displaced in an axial direction DA about the rotational center axis CA of the front sprocket 6.

Referring to FIG. 4 , the compound rear sprocket assembly 16 will be described. FIG. 4 shows a schematic diagram of the compound rear sprocket assembly 16 and illustrates the arrangement relationship between the compound rear sprocket assembly 16 and the front sprocket 6 in the axial direction DA.

Each of the plurality of rear sprockets 8 has an axially outer portion 30 and an axially inner portion 32 relative to the rotational axis CA. An axial length LA, defined in the axial direction DA as the length between the axially outer portion 30 of the smallest rear sprocket 22 and the axially inner portion 32 of the largest rear sprocket 24, is preferably 47.5 mm or greater.

The axial length LA is preferably 48 mm or greater. Furthermore, the axial length LA is preferably 49 mm or greater.

The tooth ratio of the largest rear sprocket 24 to the smallest rear sprocket 22 is preferably 3.4 or greater.

The sprocket density is defined as the value obtained by dividing the total number of rear sprockets 8 by the axial length LA. In this embodiment, the sprocket density is preferably 0.28 or greater.

The smallest rear sprocket 22 preferably has a total number of 12 or fewer teeth, and the largest rear sprocket 24 preferably has a total number of 42 or more teeth. For example, the smallest rear sprocket 22 has a total number of 9, 10, 11, or 12 teeth. The largest rear sprocket 24 has a total number of 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, or 52 teeth. The total number of teeth on the multiple rear sprockets 8 is preferably 14 or more.

The following are two examples of combining the full number of teeth of the front sprocket 6 with the full number of teeth of each rear sprocket 8 of the compound rear sprocket assembly 16.

The first example is as follows. The total number of teeth on the front sprocket 6 is 58. The total number of teeth on each rear sprocket 8 in the compound rear sprocket assembly 16 is 12, 13, 14, 15, 17, 19, 21, 23, 25, 28, 31, 34, 38, and 42, respectively. The total number of rear sprockets 8 in the compound rear sprocket assembly 16 is 14. The gear ratio is 3.5.

The second example is as follows. The total number of teeth on the front sprocket 6 is 43. The total number of teeth on each rear sprocket 8 in the compound rear sprocket assembly 16 is 10, 11, 13, 15, 17, 19, 21, 23, 26, 29, 33, 37, 42, and 47, respectively. The total number of rear sprockets 8 in the compound rear sprocket assembly 16 is 14. The gear ratio is 4.7.

The front sprocket 6 is preferably a single front sprocket. The axial displacement width RD of the front sprocket 6 relative to the crank arm 4 caused by the sprocket gear shifting mechanism 20 is in the range of 5mm to 30mm. The axial displacement width RD is preferably 7mm to 10mm.

As shown in FIG. 1 , when the bicycle drive system 12 is mounted on the bicycle A and the front sprocket 6 is positioned at the axial center point PCR by the total axial displacement width RD of the front sprocket 6 relative to the crank arm 4 caused by the sprocket gear shifting mechanism 20, at least five intermediate rear sprockets 26 are preferably positioned in the axial direction DA between the largest rear sprocket 24 and the axial center plane PCS of the front sprocket 6. More preferably, at least six intermediate rear sprockets 26 are positioned in the axial direction DA between the largest rear sprocket 24 and the axial center plane PCS of the front sprocket 6. In the embodiment shown in FIG. 4 , the six intermediate rear sprockets 26 are positioned in the axial direction DA between the largest rear sprocket 24 and the axial center plane PCS of the front sprocket 6.

The bicycle drive system 12 of this embodiment preferably employs at least one of the structures of the second to fifth embodiments described below.

The function of the sprocket gear shifting mechanism 20 is explained.

The sprocket carrier 42 is displaceable relative to the crank arm 4 in the axial direction DA about the rotational axis CA of the front sprocket 6. When the multiple rear sprocket assembly 16 is shifting while the bicycle A is in motion, a force in the axial direction DA about the rotational axis CA acts on the front sprocket 6 via the bicycle chain 10. The sprocket carrier 42 then moves in the same direction as the bicycle chain 10. This reduces the inclination of the bicycle chain 10 with respect to the center plane CS of the bicycle A, improving driving efficiency and preventing chain dropout. This action allows the multiple rear sprocket assembly 16 to accommodate a greater number of rear sprockets 8.

The bicycle drive system 12 includes a sprocket gear shifting mechanism 20 and a multiple rear sprocket assembly 16 including at least 14 rear sprockets 8. By including the sprocket gear shifting mechanism 20 and at least 14 rear sprockets 8, the bicycle drive system 12 can prevent chain slippage and smoothly change gear ratios over a wide range.

<Second Implementation Method>

The following describes a bicycle front sprocket assembly 34 including the sprocket gear shifting mechanism 20.

The bicycle front sprocket assembly 34 includes a front sprocket 6 and a sprocket gear shifting mechanism 20.

The front sprocket 6 includes a sprocket body 36 and a plurality of sprocket teeth 18 arranged on the outer periphery of the sprocket body 36.

The front sprocket 6 has a first axial surface 38 and a second axial surface 40 (see FIG. 10 ) located opposite the first axial surface 38 in the axial direction DA. The second axial surface 40 faces the center plane CS of the bicycle A when the bicycle front sprocket assembly 34 is mounted on the bicycle A.

The sprocket gear shifting mechanism 20 includes a sprocket carrier 42 coupled to the front sprocket 6 and a base member 44 coupled to either the crank arm 4 or the crank axle 2.

When the bicycle front sprocket assembly 34 is assembled to the crank axle 2 and crank arm 4, the sprocket gear shifting mechanism 20 allows the plurality of sprocket gears 18 of the front sprocket 6 to be shifted in at least one of the crank arm 4 and crank axle 2 in the axial direction DA about the rotational axis CA of the front sprocket 6, and allows the sprocket carrier 42 to move relative to the base member 44.

An example of the sprocket gear shifting mechanism 20 will be described with reference to Figures 5 to 12. Figure 5 is a perspective view of an assembly comprising the sprocket gear shifting mechanism 20, the crankshaft 2, the crank arm 4, and the front sprocket 6. Figure 6 is a side view of the assembly. Figure 7 is an exploded perspective view of the assembly. Figure 8 is an exploded perspective view of the sprocket gear shifting mechanism 20. Figure 9 is an exploded perspective view of the sliding portion 52 and the retaining member 54. Figure 10 is a cross-sectional view taken along line X-X of Figure 6. Figure 11 is an enlarged view of a portion of Figure 10.

The base member 44 is mounted on either the crankshaft 2 or the crank arm 4. Alternatively, the base member 44 can be removably connected to either the crankshaft 2 or the crank arm 4 via a splined engagement. In this case, the sprocket gear shifting mechanism 20 preferably further includes a locking member 46. The locking member 46 is engaged with either the crank arm 4 or the crankshaft 2 to prevent displacement of the base member 44 relative to either the crank arm 4 or the crankshaft 2 in the assembled state.

In this embodiment, the base member 44 is detachably connected to the crank arm 4 by spline engagement.

As shown in Figures 10 and 11, the crank arm 4 includes an insertion hole 4a through which the crank axle 2 is inserted, and a cylindrical protrusion 4b surrounding one end of the insertion hole 4a. The protrusion 4b of the crank arm 4 is formed with a spline 4d that, when assembled, is parallel to the axial direction DA along the rotational axis CA of the front sprocket 6.

As shown in Figure 11, the base member 44 includes a main body 48 surrounding the base end 4c of the crank arm 4, and a mounting portion 50 provided on the main body 48 and mounted on the protruding portion 4b of the crank arm 4. As shown in Figure 8, at least one first sliding surface 51 is provided on the main body 48 of the base member 44. A groove is formed in the mounting portion 50 of the base member 44 for engaging with the spline 4d of the crank arm 4.

As shown in Figure 10 , the base member 44 is secured to the crank arm 4 via a locking member 46 . The locking member 46 is used to prevent displacement of the base member 44 relative to the crank arm 4 during assembly, and engages with either the crank arm 4 or the crank axle 2 . The locking member 46 may be comprised of a single component or multiple components.

In this embodiment, the sliding portion 52 includes a first sliding surface 51, a second sliding surface 61, and a sliding body 53.

The first sliding surface 51 of the base member 44 is used to support the sliding body 53. In this embodiment, the sliding body 53 is a rolling body composed of, for example, steel balls. The sliding body 53 may also be a needle-shaped rolling body.

As shown in Figure 9, the slider 53 is held by a retaining member 54. The first sliding surface 51 of the base member 44 slides against the slider 53, allowing the base member 44 to move in the axial direction DA about the rotational axis CA of the front sprocket 6 relative to the sprocket carrier 42. The retaining member 54 includes four retaining portions 56 that rotatably retain the slider 53. The retaining portions 56 include a first surface portion 56a of the base member 44 that faces the first sliding surface 51 and a second surface portion 56b that faces the second sliding surface 61 provided on the sprocket carrier 42. Holes 56c for receiving the slider 53 are provided in the first and second surface portions 56a, 56b.

The sliding portion 52 may also be a sliding bearing structure in which the sliding body 53 is omitted and the first sliding surface 51 and the second sliding surface 61 slide directly.

As shown in Figure 5 , the front sprocket 6 is mounted on the sprocket carrier 42. The sprocket carrier 42 includes a main body 58 surrounding the base member 44 and a connecting portion 60 provided on the main body 58 and connected to the front sprocket 6. At least one second sliding surface 61 is provided on the main body 58 of the sprocket carrier 42. The main body 58 has a through-hole 58a through which the end of the crankshaft 2 is inserted. The second sliding surface 61 is provided on the inner circumferential surface 58b of the main body 58. A recess 58c extending from the outer surface toward the inner surface in the axial direction DA is provided in the main body 58. The recess 58c is used to accommodate a portion of the crank arm 4. The second sliding surface 61 slides with the slider 53. The second sliding surface 61 slides with the sliding body 53 relative to the base member 44 and is movable in the axial direction DA about the rotational axis CA of the front sprocket 6. The driving force of the crankshaft 2 is transmitted to the sprocket carrier 42 via the sliding body 53.

As shown in Figures 5 and 6 , in this embodiment, the sprocket carrier 42 is fastened to the front sprocket 6 via a fastening member 64. A cover mounting member 66 for mounting a dust cover 68 is mounted on the sprocket carrier 42. After the cover mounting member 66 is mounted radially outward of the dust cover 68, the fastening member 64 is fastened to the connecting portions 60 and 70. The head of the fastening member 64 and the sprocket carrier 42 sandwich the cover mounting member 66, securing the cover mounting member 66.

The connection between the sprocket carrier 42 and the front sprocket 6 can also be configured as follows. A protrusion is provided on one of the sprocket carrier 42 and the front sprocket 6 to engage with a recess or through-hole provided on the other. The sprocket carrier 42 and the front sprocket 6 are connected by a return stitch on the protrusion.

As shown in Figures 5 and 6 , the sprocket gear shifting mechanism 20 is preferably further covered by a dustproof cover 68. The dustproof cover 68 includes at least a first cover portion 68a and a second cover portion 68b. The first cover portion 68a is positioned on the first axial surface 38 of the front sprocket 6, in the axial direction DA of the rotational axis CA of the front sprocket 6. The first cover portion 68a covers the gap between the sprocket carrier 42 and the base member 44, as well as the sliding portion 52. The second cover portion 68b is positioned on the second axial surface 40 of the front sprocket 6, in the axial direction DA of the rotational axis CA of the front sprocket 6. The second cover portion 68b covers the gap between the sprocket carrier 42 and the base member 44, as well as the sliding portion 52.

Referring to Figures 12 to 14, the fastening structure between the front sprocket 6 and the sprocket carrier 42 is described. Figure 12 is a side view of the front sprocket 6. Figure 13 is a side view of the sprocket carrier 42. Figure 14 is a side view of the assembly of the front sprocket 6 and the sprocket carrier 42.

The sprocket body 36 includes a first connecting portion 70A having a first fastening axis AF1, a second connecting portion 70B having a second fastening axis AF2, a third connecting portion 70C having a third fastening axis AF3, and a fourth connecting portion 70D having a fourth fastening axis AF4.

The sprocket carrier 42 includes a fifth connecting portion 60E having a fifth fastening axis AF5, a sixth connecting portion 60F having a sixth fastening axis AF6, a seventh connecting portion 60G having a seventh fastening axis AF7, and an eighth connecting portion 60H having an eighth fastening axis AF8.

The second connecting portion 70B is separated from the first connecting portion 70A in the circumferential direction DC about the rotational axis CA of the front sprocket 6, with no other connecting portions 70C or 70D between them.

The third connecting portion 70C is separated from the second connecting portion 70B in the circumferential direction DC and there are no other connecting portions 70A or 70D between them.

The fourth link 70D is separated from the first link 70A and the third link 70C in the circumferential direction DC, with no other link 70B between them. In the assembled state, the crank arm 4 is positioned between the first link 70A and the fourth link 70D in the circumferential direction DC.

The sixth connecting portion 60F is separated from the fifth connecting portion 60E in the circumferential direction DC and has no other connecting portions 60G or 60H between them.

The seventh connecting portion 60G is separated from the sixth connecting portion 60F in the circumferential direction DC and there are no other connecting portions 60E or 60H between them.

The eighth link 60H is separated from the fifth link 60E and the seventh link 60G in the circumferential direction DC, with no other link 60F between them. In the assembled state, the crank arm 4 is positioned between the fifth link 60E and the eighth link 60H in the circumferential direction DC.

The first fastening axis AF1 of the first connecting portion 70A and the fifth fastening axis AF5 of the fifth connecting portion 60E are aligned with each other relative to the first common axis AC1, allowing the first fastening member 64A to pass through at least one of the first connecting portion 70A and the fifth connecting portion 60E.

The second fastening axis AF2 of the second connecting portion 70B and the sixth fastening axis AF6 of the sixth connecting portion 60F are aligned with each other relative to the second common axis AC2, allowing the second fastening member 64B to pass through at least one of the second connecting portion 70B and the sixth connecting portion 60F.

The third fastening axis AF3 of the third connecting portion 70C and the seventh fastening axis AF7 of the seventh connecting portion 60G are aligned with each other relative to the third common axis AC3, allowing the third fastening member 64C to pass through at least one of the third connecting portion 70C and the seventh connecting portion 60G.

The fourth fastening axis AF4 of the fourth connecting portion 70D and the eighth fastening axis AF8 of the eighth connecting portion 60H are aligned relative to the fourth common axis AC4, allowing the fourth fastening member 64D to pass through at least one of the fourth connecting portion 70D and the eighth connecting portion 60H.

The first connection angle AG1 is defined as the angle between a first reference line LR1 extending from the rotation center axis CA toward the first common axis AC1 and a second reference line LR2 extending from the rotation center axis CA toward the second common axis AC2 in the circumferential direction DC, so that the other common axes AC3 and AC4 are not located between the first common axis AC1 and the second common axis AC2 in the circumferential direction DC.

The second connection angle AG2 is defined as the angle between the second reference line LR2 in the circumferential direction DC and the third reference line LR3 extending from the rotation center axis CA toward the third common axis AC3, so that the other common axes AC1 and AC4 are not located between the second common axis AC2 and the third common axis AC3 in the circumferential direction DC.

The third connection angle AG3 is defined as the angle between the third reference line LR3 in the circumferential direction DC and the fourth reference line LR4 extending from the rotation center axis CA toward the fourth common axis AC4, so that the other common axes AC1 and AC2 are not located between the third common axis AC3 and the fourth common axis AC4 in the circumferential direction DC.

The fourth connection angle AG4 is defined as the angle between the fourth reference line LR4 and the first reference line LR1 in the circumferential direction DC, so that the other common axes AC2 and AC3 are not located between the fourth common axis AC4 and the first common axis AC1 in the circumferential direction DC.

At least one of the first connection angle AG1, the second connection angle AG2, the third connection angle AG3, and the fourth connection angle AG4 is different from another of the first connection angle AG1, the second connection angle AG2, the third connection angle AG3, and the fourth connection angle AG4.

It is preferred that the first connection angle AG1 is smaller than the second connection angle AG2 and the fourth connection angle AG4.

It is preferred that the third connection angle AG3 is smaller than the second connection angle AG2 and the fourth connection angle AG4.

It is preferred that the first connection angle AG1 and the third connection angle AG3 be equal.

It is preferred that the second connection angle AG2 and the fourth connection angle AG4 are different. It is also preferred that the second connection angle AG2 is smaller than the fourth connection angle AG4.

When viewed in the axial direction DA from the first axial surface 38 toward the second axial surface 40 (see FIG. 10 ), the first common axis AC1 to the fourth common axis AC4 are preferably arranged in the order of the first common axis AC1 to the fourth common axis AC4 in the counterclockwise direction CCW from the crank arm 4 in the circumferential direction DC.

Figure 15 is a side view of the assembly of the front sprocket 6, sprocket carrier 42, base member 44, and crank arm 4. As shown in Figure 13, in one example, the first connecting portion 70A to the fourth connecting portion 70D of the front sprocket 6 are arranged radially outward of the sliding portion 52 relative to the rotational axis CA of the front sprocket 6.

Referring to Figure 16, the operation of the sprocket gear shifting mechanism 20 of this embodiment will be described.

The sprocket carrier 42 is displaceable relative to the base member 44 mounted on the crank arm 4 in the axial direction DA about the rotational axis CA of the front sprocket 6. When the multiple rear sprocket assembly 16 is shifted while the bicycle A is in motion, a force in the axial direction DA about the rotational axis CA is applied to the front sprocket 6 via the bicycle chain 10. Consequently, the sprocket carrier 42 moves in the same direction as the bicycle chain 10.

The function of the bicycle front sprocket assembly 34 is described.

The driving force from either the crank arm 4 or the crank axle 2 is transmitted from the base member 44 to the front sprocket 6 via the sprocket carrier 42. The sprocket carrier 42 is connected to the front sprocket 6 at four locations. As described above, at least one of the first connection angle AG1, the second connection angle AG2, the third connection angle AG3, and the fourth connection angle AG4 is different from another of the first connection angle AG1, the second connection angle AG2, the third connection angle AG3, and the fourth connection angle AG4. When the right crank arm 4 is pedaled to drive the bicycle, the tension of the bicycle chain 10 strongly acts on the sprocket teeth located between the first reference line LR1 and the second reference line LR2 defining the first connection angle AG1. By reducing the first connection angle AG1, the rigidity of the bicycle front sprocket assembly 34 can be improved when the right crank arm 4 is pedaled. When the left crank arm 4 is pedaled, the tension of the bicycle chain 10 acts strongly on the sprocket teeth located between the third reference line LR3 and the fourth reference line LR4, which define the third connection angle AG3. By reducing the third connection angle AG3, the rigidity of the bicycle front sprocket assembly 34 can be improved when the left crank arm 4 is pedaled. Therefore, by reducing at least one of the first connection angle AG1 and the third connection angle AG3, or more preferably, reducing both the first connection angle AG1 and the third connection angle AG3, driving efficiency can be improved.

<Third Implementation Method>

Referring to FIG. 15 , a bicycle front sprocket assembly 34 including an example of a sprocket gear shifting mechanism 20 will be described. Components common to the second embodiment are denoted by the same reference numerals as those in the second embodiment, and repeated descriptions will be omitted.

The bicycle front sprocket assembly 34 includes a front sprocket 6 and a sprocket gear shifting mechanism 20.

The front sprocket 6 includes a sprocket body 36 and a plurality of sprocket teeth 18 arranged on the outer periphery of the sprocket body 36.

The front sprocket 6 has a first axial surface 38 and a second axial surface 40 located on the opposite side of the first axial surface 38 in the axial direction DA. The second axial surface 40 faces the center plane CS of the bicycle A when the bicycle front sprocket assembly 34 is mounted on the bicycle A.

The sprocket gear shifting mechanism 20 includes a sprocket carrier 42 coupled to the front sprocket 6 and a base member 44 coupled to either the crank arm 4 or the crank axle 2.

When the bicycle front sprocket assembly 34 is assembled to the crank axle 2 and crank arm 4, the sprocket gear shifting mechanism 20 allows the plurality of sprocket gears 18 of the front sprocket 6 to be shifted in at least one of the crank arm 4 and crank axle 2 in the axial direction DA about the rotational axis CA of the front sprocket 6, and allows the sprocket carrier 42 to move relative to the base member 44.

The structure of the sprocket gear shifting mechanism 20 is the same as that of the second embodiment. The fastening structure between the front sprocket 6 and the base member 44 is not limited. It is preferred that the fastening structure between the front sprocket 6 and the base member 44 be the same as that exemplified in the second embodiment.

The base member 44 is mounted on either the crankshaft 2 or the crank arm 4. The base member 44 can also be detachably connected to either the crankshaft 2 or the crank arm 4 by spline engagement.

The sprocket gear shifting mechanism 20 includes a first sliding portion 52A having a first sliding center point PS1, a second sliding portion 52B having a second sliding center point PS2, a third sliding portion 52C having a third sliding center point PS3, and a fourth sliding portion 52D having a fourth sliding center point PS4.

The second sliding portion 52B is separated from the first sliding portion 52A in the circumferential direction DC about the rotational axis CA of the front sprocket 6, with no other sliding portion 52 between them. The third sliding portion 52C is separated from the second sliding portion 52B in the circumferential direction DC, with no other sliding portion 52 between them.

The fourth sliding portion 52D is separated from the first sliding portion 52A and the third sliding portion 52C in the circumferential direction DC, with no other sliding portion 52 between them. In the assembled state, the crank arm 4 is positioned between the first sliding portion 52A and the fourth sliding portion 52D in the circumferential direction DC.

The first sliding angle AGS1 is defined as the angle between the first sliding reference line PRS1 extending from the rotation axis CA toward the first sliding center point PS1 and the second sliding reference line PRS2 extending from the rotation axis CA toward the second sliding center point PS2 in the circumferential direction DC, so that the other sliding center points PS3 and PS4 are not located between the first sliding center point PS1 and the second sliding center point PS2 in the circumferential direction DC.

The second sliding angle AGS2 is defined as the angle between the second sliding reference line PRS2 in the circumferential direction DC and the third sliding reference line PRS3 extending from the rotational axis CA toward the third sliding center point PS3, so that the other sliding center points PS1 and PS4 are not located between the second sliding center point PS2 and the third sliding center point PS3 in the circumferential direction DC.

The third sliding angle AGS3 is defined as the angle between the third sliding reference line PRS3 and the fourth sliding reference line PRS4 extending from the rotation axis CA toward the fourth sliding center point PS4 in the circumferential direction DC, so that the other sliding center points PS1 and PS2 are not located between the third sliding center point PS3 and the fourth sliding center point PS4 in the circumferential direction DC.

The fourth sliding angle AGS4 is defined as the angle between the fourth sliding reference line PRS4 and the first sliding reference line PRS1 in the circumferential direction DC, so that the other sliding center points PS2 and PS3 are not located between the fourth sliding center point PS4 and the first sliding center point PS1 in the circumferential direction DC.

At least one of the first sliding angle AGS1, the second sliding angle AGS2, the third sliding angle AGS3, and the fourth sliding angle AGS4 is different from another one of the first sliding angle AGS1, the second sliding angle AGS2, the third sliding angle AGS3, and the fourth sliding angle AGS4.

It is preferred that the first sliding angle AGS1 is smaller than the second sliding angle AGS2 and the fourth sliding angle AGS4.

It is preferred that the third sliding angle AGS3 is smaller than the second sliding angle AGS2 and the fourth sliding angle AGS4.

It is preferred that the first sliding angle AGS1 and the third sliding angle AGS3 are equal.

It is preferred that the second sliding angle AGS2 and the fourth sliding angle AGS4 are different. It is also preferred that the second sliding angle AGS2 is smaller than the fourth sliding angle AGS4.

When viewed in the axial direction DA from the first axial surface 38 toward the second axial surface 40, the first sliding center point PS1 to the fourth sliding center point PS4 are preferably arranged in the order of the first sliding center point PS1 to the fourth sliding center point PS4 in the counterclockwise direction CCW from the crank arm 4 in the circumferential direction DC.

The operation of the sprocket gear shifting mechanism 20 of this embodiment is the same as that of the sprocket gear shifting mechanism 20 of the second embodiment.

The function of the bicycle front sprocket assembly 34 is described.

The driving force of one of the crank arm 4 and the crank axle 2 is transmitted from the base member 44 to the front sprocket 6 via the sprocket carrier 42. The base member 44 slides on the sprocket carrier 42 at four locations. As described above, at least one of the first sliding angle AGS1, the second sliding angle AGS2, the third sliding angle AGS3, and the fourth sliding angle AGS4 is different from another of the first sliding angle AGS1, the second sliding angle AGS2, the third sliding angle AGS3, and the fourth sliding angle AGS4. When the right crank arm 4 is pedaled to drive the bicycle, the tension of the bicycle chain 10 strongly acts on the sprocket teeth located between the first reference line LR1 and the second reference line LR2, which define the first connection angle AG1. By reducing the first sliding angle AGS1, the rigidity of the sliding portion 52 can be increased when the right crank arm 4 is pedaled. When the left crank arm 4 is pedaled, the tension of the bicycle chain 10 acts strongly on the sprocket teeth located between the third reference line LR3 and the fourth reference line LR4, which define the third connection angle AG3. By reducing the third sliding angle AGS3, the rigidity of the sliding portion 52 can be increased when the left crank arm 4 is pedaled. Therefore, by reducing at least one of the first sliding angle AGS1 and the third sliding angle AGS3, or more preferably, reducing both the first sliding angle AGS1 and the third sliding angle AGS3, the rigidity of the sprocket tooth shifting mechanism can be improved.

<Fourth Implementation Method>

Referring to FIG. 17 , a bicycle front sprocket assembly 34 including an example of a sprocket gear shifting mechanism 20 will be described. Components common to the second embodiment are denoted by the same reference numerals as those in the second embodiment, and repeated descriptions will be omitted.

The bicycle front sprocket assembly 34 includes a front sprocket 6 and a sprocket gear shifting mechanism 20.

The front sprocket 6 includes a sprocket body 36 and a plurality of sprocket teeth 18 arranged on the outer periphery of the sprocket body 36.

The sprocket gear shifting mechanism 20 includes a sprocket carrier 42 coupled to the front sprocket 6 and a base member 44 coupled to either the crank arm 4 or the crank axle 2.

When the bicycle front sprocket assembly 34 is assembled to the crank axle 2 and crank arm 4, the sprocket gear shifting mechanism 20 allows the plurality of sprocket gears 18 of the front sprocket to be shifted in the axial direction DA about the rotational axis CA of the front sprocket 6 relative to either the crank arm 4 or the crank axle 2, and allows the sprocket carrier 42 to move relative to the base member 44.

The structure of the sprocket gear shifting mechanism 20 is the same as that of the second embodiment. The fastening structure between the front sprocket 6 and the base member 44 is not limited. Preferably, the fastening structure between the front sprocket 6 and the base member 44 is the same as that of the second embodiment. The sliding structure between the base member 44 and the sprocket carrier 42 is not limited. Preferably, the sliding structure between the base member 44 and the sprocket carrier 42 is the same as that of the third embodiment.

The base member 44 is mounted on either the crankshaft 2 or the crank arm 4. The base member 44 can also be detachably connected to either the crankshaft 2 or the crank arm 4 by spline engagement.

The sprocket body 36 includes at least one connecting portion 70X. The sprocket carrier 42 includes at least one additional connecting portion 60X.

At least one connecting portion 70X of the sprocket body 36 and at least one additional connecting portion 60X of the sprocket carrier 42 are coupled to each other via at least one fastening member 64.

The sprocket gear shifting mechanism 20 includes at least one sliding portion 52. The total number of the at least one fastening member 64 is equal to the total number of the at least one sliding portion 52.

The at least one connecting portion 70X of the sprocket body 36 includes a plurality of connecting portions. The at least one additional connecting portion 60X of the sprocket body 42 includes a plurality of connecting portions.

The at least one fastening member 64 includes a plurality of fastening members 64A, 64B, 64C, and 64D. The at least one sliding portion 52 includes a plurality of sliding portions 52. The total number of the plurality of fastening members is equal to the total number of the plurality of sliding portions 52.

At least one sliding portion 52 is disposed near at least one fastening member 64 in the assembled state.

In the assembled state, at least one sliding portion 52 is positioned upstream of at least one fastening member 64 in the driving rotational direction.

The operation of the sprocket gear shifting mechanism 20 of this embodiment is the same as that of the sprocket gear shifting mechanism 20 of the second embodiment.

The function of the bicycle front sprocket assembly 34 is described.

The driving force from either the crank arm 4 or the crankshaft 2 is transmitted from the base member 44 to the front sprocket 6 via the sprocket carrier 42. The base member 44 slides on the sprocket carrier 42 at four locations. As described above, in the sprocket gear shifting mechanism 20, at least one connecting portion 70X of the front sprocket 6 and at least one additional connecting portion 60X of the sprocket carrier 42 are coupled together via at least one fastening member 64. The total number of the at least one fastening member 64 is equal to the total number of the at least one sliding portion 52. Thus, the driving force is transmitted from the base member 44 to the sprocket carrier 42 via the sliding portion 52 and the fastening member 64. The corresponding relationship between the sliding portion 52 and the fastening member 64 effectively transmits the driving force to the sprocket carrier 42. This effectively transmits the driving force from the crankshaft 2 to the sprocket.

<Fifth Implementation Method>

Referring to Figures 18 to 23 , a bicycle front sprocket assembly 34 including an example of the sprocket gear shifting mechanism 20 will be described. Components common to the second embodiment are denoted by the same reference numerals as those in the second embodiment, and repeated descriptions will be omitted.

The bicycle front sprocket assembly 34 includes a front sprocket 6 and a sprocket gear shifting mechanism 20.

The front sprocket 6 includes a sprocket body 36 and a plurality of sprocket teeth 18 arranged on the outer periphery of the sprocket body 36 in the circumferential direction DC about the rotational center axis CA of the front sprocket 6.

The sprocket gear shifting mechanism 20 includes a sprocket carrier 42 coupled to the front sprocket 6, and a base member 44 coupled to either the crank arm 4 or the crank axle 2 via a groove.

When the bicycle front sprocket assembly 34 is assembled to the crank axle 2 and crank arm 4, the sprocket gear shifting mechanism 20 allows the plurality of sprocket gears 18 of the front sprocket to be shifted in the axial direction DA about the rotational axis CA of the front sprocket 6 relative to either the crank arm 4 or the crank axle 2, and allows the sprocket carrier 42 to move relative to the base member 44.

The structure of the sprocket gear shifting mechanism 20 is the same as that of the second embodiment. The fastening structure between the front sprocket 6 and the base member 44 is not limited. Preferably, the fastening structure between the front sprocket 6 and the base member 44 is the same as that of the second embodiment. The sliding structure between the base member 44 and the sprocket carrier 42 is not limited. Preferably, the sliding structure between the base member 44 and the sprocket carrier 42 is the same as that of the third embodiment.

The base member 44 is mounted on either the crankshaft 2 or the crank arm 4. The base member 44 can also be detachably connected to either the crankshaft 2 or the crank arm 4 by spline engagement.

As shown in Figures 19 and 20, the plurality of sprocket teeth 18 include at least one first tooth 82 having a first maximum chain engagement axial width WA1 relative to the rotational axis CA, and at least one second tooth 84 having a second maximum chain engagement axial width WA2 relative to the rotational axis CA. In the axial direction DA of the rotational axis CA, the first maximum chain engagement axial width WA1 is greater than the second maximum chain engagement axial width WA2.

A locking member 46 is further provided. The locking member 46 is used to prevent displacement of the base member 44 relative to one of the crank arm 4 and the crank axle 2 when assembled, thereby engaging with the crank arm 4 and the crank axle 2.

As shown in Figure 18, the first radial length LRS1 is defined as the length between the first radial outermost tooth end 82a of at least one first tooth 82 in the radial direction of the rotation axis CA and the rotation axis CA. The second radial length LRS2 is defined as the length between the second radial outermost tooth end 84a of at least one second tooth 84 in the radial direction of the rotation axis CA and the rotation axis CA. The first radial length LRS1 is longer than the second radial length LRS2.

As shown in Figure 21, the first maximum chain engagement axial width WA1 is greater than the inner connecting rod axial spacing WAI defined between a pair of inner connecting rods 92 of the bicycle chain 10 in the axial direction DA, and less than the outer connecting rod axial spacing WAJ defined between a pair of outer connecting rods 94 of the bicycle chain 10 in the axial direction DA. The second maximum chain engagement axial width WA2 is less than the inner connecting rod axial spacing WAI.

The first maximum chain engagement axial width WA1 of at least one first tooth 82 is preferably at least 75% of the outer connecting rod axial spacing WAJ. More preferably, the first maximum chain engagement axial width WA1 of at least one first tooth 82 is at least 80% of the outer connecting rod axial spacing WAJ.

As shown in FIG. 19 , at least one first tooth 82 has a first axial tooth end centerline LCRT1 that is offset from a first axial tooth center plane CST1 of the at least one first tooth 82 in the axial direction DA.

As shown in FIG. 20 , at least one second tooth 84 has a second axial tooth end centerline LCRT2 that is offset from a second axial tooth center plane CST2 of the at least one second tooth 84 in the axial direction DA.

As shown in Figure 22, at least one first tooth 82 is asymmetrical in the circumferential direction DC relative to the first circumferential tooth base centerline LCT1. Specifically, the driving surface of the first tooth 82 may be different in size or shape from the non-driving surface of the first tooth 82. In this embodiment, the chamfer of the driving surface of the first tooth 82 is larger than the chamfer of the non-driving surface of the first tooth 82. In other examples, the curvature of the driving surface of the first tooth 82 may be different from the curvature of the non-driving surface.

As shown in Figure 23 , at least one second tooth 84 is asymmetrical in the circumferential direction DC relative to the second circumferential tooth base centerline LCT2. Specifically, the driving surface of the second tooth 84 may be different in size or shape from the non-driving surface of the second tooth 84. In this embodiment, a notch is formed on the driving surface at the tooth end of the second tooth 84, while no notch is formed on the non-driving surface at the tooth end of the second tooth 84. In other examples, the curvature of the driving surface of the second tooth 84 may be different from the curvature of the non-driving surface.

As shown in Figure 19, at least one first tooth 82 is asymmetric in the axial direction DA relative to the first circumferential tooth bottom center plane CST1.

As shown in Figure 20, at least one second tooth 84 is asymmetric in the axial direction DA relative to the second circumferential tooth bottom center plane CST2.

The at least one first tooth 82 includes a plurality of first teeth 82. The at least one second tooth 84 includes a plurality of second teeth 84. The plurality of first teeth 82 and the plurality of second teeth 84 are alternately arranged in a DC pattern in the circumferential direction.

The operation of the sprocket gear shifting mechanism 20 of this embodiment is the same as that of the sprocket gear shifting mechanism 20 of the second embodiment.

The function of the bicycle front sprocket assembly 34 is described.

The driving force from either the crank arm 4 or the crank axle 2 is transmitted from the sprocket to the multiple rear sprocket assembly 16 via the bicycle chain 10. The sprocket is shifted in the axial direction DA about the rotational axis CA by the sprocket gear shifting mechanism 20. As described above, the plurality of sprocket gears 18 include at least one first tooth 82 having a first maximum chain engagement axial width WA1 relative to the rotational axis CA, and at least one second tooth 84 having a second maximum chain engagement axial width WA2 relative to the rotational axis CA. In the axial direction DA of the rotational axis CA, the first maximum chain engagement axial width WA1 is greater than the second maximum chain engagement axial width WA2. This structure increases the engagement force with the bicycle chain 10. In particular, when the sprocket moves in the axial direction DA of the rotational axis CA, the increased engagement force between the sprocket and the bicycle chain 10 prevents chain slippage and improves driving efficiency.

A: Bicycle

CA: Center of rotation axis

CS: Center plane

DA: axis direction

PCR: Axial Center Point

1: Framework

2: Crankshaft

4: Crank Arm

6: Front sprocket

8:Rear sprocket

10: Bicycle chain

12: Bicycle drive system

14: Crank assembly

16: Compound rear sprocket assembly

18: Sprocket gear

20: Sprocket gear shift mechanism

Claims (34)

A front sprocket assembly for a bicycle comprises a front sprocket and a sprocket gear shifting mechanism. The front sprocket includes a sprocket body and a plurality of sprocket gears disposed on the outer periphery of the sprocket body. The sprocket body includes a first connecting portion having a first fastening axis, a second connecting portion having a second fastening axis, a third connecting portion having a third fastening axis, and a fourth connecting portion having a fourth fastening axis. The sprocket gear shifting mechanism includes a sprocket carrier and a base member. The sprocket carrier is coupled to the front sprocket; the base member is coupled to either a crank arm or a crank axle. The sprocket gear shifting mechanism, when the bicycle front sprocket assembly is assembled to the crank axle and the crank arm, allows the plurality of sprocket gears of the front sprocket to be shifted relative to at least one of the crank arm and the crank axle in the axial direction of the rotational center axis of the front sprocket. Furthermore, the sprocket carrier is movable relative to the base member. The sprocket carrier includes a fifth connecting portion having a fifth fastening axis, a sixth connecting portion having a sixth fastening axis, a seventh connecting portion having a seventh fastening axis, and an eighth connecting portion having an eighth fastening axis. The second link is spaced apart from the first link in a circumferential direction about the rotational axis of the front sprocket, with no other link therebetween. The third link is spaced apart from the second link in the circumferential direction, with no other link therebetween. The fourth link is spaced apart from the first and third links in the circumferential direction, with no other link therebetween. In the assembled state, the crank arm is positioned circumferentially between the first and fourth links. The sixth link is spaced apart from the fifth link in the circumferential direction, with no other link therebetween. The seventh link is spaced apart from the sixth link in the circumferential direction, with no other link therebetween. The eighth connection portion is circumferentially spaced from the fifth and seventh connection portions, respectively, with no other connection portions therebetween. In the assembled state, the crank arm is positioned circumferentially between the fifth and eighth connection portions. The first fastening axis of the first connection portion and the fifth fastening axis of the fifth connection portion are aligned relative to a first common axis, allowing the first fastening member to pass through at least one of the first and fifth connection portions. The second fastening axis of the second connecting portion and the sixth fastening axis of the sixth connecting portion are aligned relative to the second common axis, allowing the second fastening member to pass through at least one of the second connecting portion and the sixth connecting portion. The third fastening axis of the third connecting portion and the seventh fastening axis of the seventh connecting portion are aligned relative to the third common axis, allowing the third fastening member to pass through at least one of the third connecting portion and the seventh connecting portion. The fourth fastening axis of the fourth connection portion and the eighth fastening axis of the eighth connection portion are aligned relative to the fourth common axis, allowing the fourth fastening member to pass through at least one of the fourth connection portion and the eighth connection portion. The first connection angle is defined as the angle between a first reference line extending from the rotation center axis toward the first common axis and a second reference line extending from the rotation center axis toward the second common axis in the circumferential direction, so that the other common axis is not located between the first common axis and the second common axis. The second connection angle is defined as the angle between the second reference line and a third reference line extending from the rotation center axis toward the third common axis in the circumferential direction, so that no other common axis lies between the second and third common axes in the circumferential direction. The third connection angle is defined as the angle between the third reference line and a fourth reference line extending from the rotation center axis toward the fourth common axis in the circumferential direction, so that no other common axis lies between the third and fourth common axes in the circumferential direction. The fourth connection angle is defined as the angle between the fourth reference line and the first reference line in the circumferential direction, so that other common axes are not located between the fourth common axis and the first common axis. At least one of the first connection angle, the second connection angle, the third connection angle, and the fourth connection angle is different from another one of the first connection angle, the second connection angle, the third connection angle, and the fourth connection angle. The bicycle front sprocket assembly of claim 1, wherein the first connection angle is smaller than the second connection angle and the fourth connection angle. In the bicycle front sprocket assembly of claim 1 or 2, the third connection angle is smaller than the second connection angle and the fourth connection angle, respectively. In the bicycle front sprocket assembly of claim 1 or 2, the first connection angle is equal to the third connection angle. In the bicycle front sprocket assembly of claim 1 or 2, the second connection angle is different from the fourth connection angle. The bicycle front sprocket assembly of claim 5, wherein the second connection angle is smaller than the fourth connection angle. The bicycle front sprocket assembly of claim 1 or 2, wherein the front sprocket comprises: a first axial surface; and a second axial surface located opposite the first axial surface in the axial direction; The second axial surface is opposed to the center plane of the bicycle when the bicycle front sprocket assembly is mounted on the bicycle; The first to fourth common axles are arranged in the order of the first to fourth common axles in the counterclockwise direction from the crank arm in the circumferential direction when viewed from the first axial surface toward the second axial surface in the axial direction. In the bicycle front sprocket assembly of claim 1 or 2, the base member is detachably connected to one of the crank axle and the crank arm by spline engagement. A front sprocket assembly for a bicycle comprises a front sprocket and a sprocket gear shifting mechanism. The front sprocket includes a sprocket body and a plurality of sprocket gears disposed on the outer periphery of the sprocket body. The sprocket gear shifting mechanism includes a sprocket carrier and a base member. The sprocket carrier is coupled to the front sprocket. The base member is coupled to either a crank arm or a crank axle. The sprocket gear shifting mechanism, when the bicycle front sprocket assembly is assembled to the crank axle and the crank arm, allows the plurality of sprocket gears of the front sprocket to be shifted relative to at least one of the crank arm and the crank axle in the axial direction of the rotational axis of the front sprocket. Furthermore, the sprocket carrier is movable relative to the base member. The sprocket gear shifting mechanism includes a first sliding portion having a first sliding center point, a second sliding portion having a second sliding center point, a third sliding portion having a third sliding center point, and a fourth sliding portion having a fourth sliding center point. The second sliding portion is spaced apart from the first sliding portion in a circumferential direction about the rotational axis of the front sprocket and has no other connection therebetween. The third sliding portion is spaced apart from the second sliding portion in the circumferential direction and has no other connection therebetween. The fourth sliding portion, in the assembled state, is configured to position the crank arm circumferentially between the first and fourth sliding portions and is spaced apart from the first and third sliding portions, respectively, in the circumferential direction and has no other connection therebetween. The first sliding angle is defined as the angle between a first sliding reference line extending from the rotational axis toward the first sliding center point and a second sliding reference line extending from the rotational axis toward the second sliding center point in the circumferential direction, so that other sliding center points are not located between the second sliding center point and the third sliding center point in the circumferential direction. The second sliding angle is defined as the angle between the second sliding reference line and a third sliding reference line extending from the rotational axis toward the third sliding center point in the circumferential direction, so that other sliding center points are not located between the second sliding center point and the third sliding center point in the circumferential direction. The third sliding angle is defined as the angle between the third sliding reference line and a fourth sliding reference line extending from the rotational axis toward the fourth sliding center point in the circumferential direction, so that other sliding center points are not located between the fourth sliding center point and the first sliding center point in the circumferential direction. The fourth sliding angle is defined as the angle between the fourth sliding reference line and the first sliding reference line in the circumferential direction, so that other sliding center points are not located between the fourth sliding center point and the first sliding center point in the circumferential direction. At least one of the first sliding angle, the second sliding angle, the third sliding angle, and the fourth sliding angle is different from another of the first sliding angle, the second sliding angle, the third sliding angle, and the fourth sliding angle. As for the front sprocket assembly for a bicycle as claimed in claim 9, the above-mentioned first sliding angle is smaller than the above-mentioned second sliding angle and the above-mentioned fourth sliding angle. As for the front sprocket assembly for a bicycle as claimed in claim 9 or 10, the above-mentioned third sliding angle is smaller than the above-mentioned second sliding angle and the above-mentioned fourth sliding angle. As for the front sprocket assembly for a bicycle as claimed in claim 9 or 10, the above-mentioned first sliding angle is equal to the above-mentioned third sliding angle. In the front sprocket assembly for a bicycle according to claim 9 or 10, the second sliding angle is different from the fourth sliding angle. A front sprocket assembly for a bicycle as claimed in claim 9 or 10, wherein the second sliding angle is smaller than the fourth sliding angle. The bicycle front sprocket assembly of claim 9 or 10, wherein the front sprocket comprises: a first axial surface; and a second axial surface located opposite the first axial surface in the axial direction; The second axial surface is opposed to the center plane of the bicycle when the bicycle front sprocket assembly is mounted on the bicycle; The first to fourth sliding center points are arranged in this order in the counterclockwise direction from the crank arm in the circumferential direction when viewed from the first axial surface toward the second axial surface in the axial direction. In the front sprocket assembly for a bicycle according to claim 9 or 10, the base member is detachably connected to one of the crank axle and the crank arm by spline engagement. A front sprocket assembly for a bicycle comprises a front sprocket and a sprocket gear shifting mechanism. The front sprocket includes a sprocket body and a plurality of sprocket gears disposed on the outer periphery of the sprocket body. The sprocket body includes at least one connecting portion. The sprocket gear shifting mechanism includes a sprocket carrier and a base member. The sprocket carrier is coupled to the front sprocket. The base member is coupled to either a crank arm or a crank axle. The sprocket gear shifting mechanism, when the bicycle front sprocket assembly is assembled to the crank axle and the crank arm, allows the plurality of sprocket gears of the front sprocket to be shifted relative to at least one of the crank arm and the crank axle in the axial direction of the rotational axis of the front sprocket. Furthermore, the sprocket carrier is movable relative to the base member. The sprocket carrier includes at least one additional connecting portion. The at least one connecting portion and the at least one additional connecting portion are coupled to each other via at least one fastening member. The sprocket gear shifting mechanism includes at least one sliding portion. The total number of the at least one fastening member is equal to the total number of the at least one sliding portion. As for the front sprocket assembly for bicycle according to claim 17, wherein the above-mentioned base member is detachably connected to the above-mentioned one of the above-mentioned crank shaft and the above-mentioned crank arm by spline engagement. The bicycle front sprocket assembly of claim 17 or 18, wherein the at least one connecting portion comprises a plurality of connecting portions, the at least one additional connecting portion comprises a plurality of connecting portions, the at least one fastening member comprises a plurality of fastening members, the at least one sliding portion comprises a plurality of sliding portions, and the total number of the plurality of fastening members is equal to the total number of the plurality of sliding portions. In the front sprocket assembly for a bicycle according to claim 17 or 18, the at least one sliding portion is arranged near at least one fastening member in the assembled state. In the front sprocket assembly for a bicycle according to claim 17 or 18, the at least one sliding portion is arranged on the upstream side of the driving rotation direction relative to the at least one fastening member in the assembled state. A front sprocket assembly for a bicycle comprises a front sprocket and a sprocket gear shifting mechanism. The front sprocket includes a sprocket body and a plurality of sprocket gears arranged on the outer periphery of the sprocket body in a circumferential direction about a rotational axis of the front sprocket. The plurality of sprocket gears include at least one first tooth having a first maximum chain engagement axial width relative to the rotational axis, and at least one second tooth having a second maximum chain engagement axial width relative to the rotational axis. In the axial direction of the rotational center axis, the first maximum chain engagement axial width is greater than the second maximum chain engagement axial width. The sprocket gear shifting mechanism comprises a sprocket carrier and a base member. The sprocket carrier is coupled to the front sprocket. The base member is coupled to either the crank arm or the crank axle via a groove engagement. When the bicycle front sprocket assembly is assembled to the crank axle and the crank arm, the sprocket gear shifting mechanism allows the plurality of sprocket gears of the front sprocket to be shifted relative to at least one of the crank arm and the crank axle in the axial direction of the rotational center axis of the front sprocket. Furthermore, the sprocket carrier is movable relative to the base member. As for the front sprocket assembly for a bicycle according to claim 22, the above-mentioned base member is detachably connected to the above-mentioned one of the above-mentioned crank shaft and the above-mentioned crank arm by spline engagement. The bicycle front sprocket assembly of claim 22 or 23 further comprises a locking member, wherein the locking member is configured to inhibit displacement of the base member relative to one of the crank arm and the crank axle in the assembled state and engage with the crank arm and the crank axle. The bicycle front sprocket assembly of claim 22 or 23, wherein the first maximum chain engagement axial width is greater than the inner link axial spacing defined between a pair of inner link plates of the axial bicycle chain and less than the outer link axial spacing defined between a pair of outer link plates of the axial bicycle chain; The second maximum chain engagement axial width is less than the inner link axial spacing. The bicycle front sprocket assembly of claim 22 or 23, wherein the first radial length is defined as the distance between the first radially outermost end of the at least one first tooth and the rotational axis in a radial direction of the rotational axis; The second radial length is defined as the distance between the second radially outermost end of the at least one second tooth relative to the rotational axis and the rotational axis; The first radial length is greater than the second radial length. A front sprocket assembly for a bicycle as claimed in claim 25, wherein the first maximum chain engagement axial width of the at least one first tooth is at least 75% of the axial spacing of the outer link. A front sprocket assembly for a bicycle as claimed in claim 22 or 23, wherein the at least one first tooth has a first axial tooth end centerline offset from a first axial tooth bottom center plane of the at least one first tooth in the axial direction. A front sprocket assembly for a bicycle as claimed in claim 22 or 23, wherein the at least one second tooth has a second axial tooth end centerline offset from a second axial tooth bottom center plane of the at least one second tooth in the axial direction. In the front sprocket assembly for a bicycle as claimed in claim 22 or 23, the at least one first tooth is asymmetrical in the circumferential direction relative to the center line of the first circumferential tooth bottom. In the front sprocket assembly for a bicycle according to claim 22 or 23, the at least one second tooth is asymmetrical in the circumferential direction relative to the center line of the second circumferential tooth bottom. As in claim 22 or 23, the front sprocket assembly for a bicycle, wherein the at least one first tooth is asymmetric in the axial direction relative to the center plane of the tooth bottom in the first axial direction. As in claim 22 or 23, the front sprocket assembly for a bicycle, wherein the at least one second tooth is asymmetric in the axial direction relative to the center plane of the tooth bottom in the second axial direction. The bicycle front sprocket assembly of claim 22 or 23, wherein the at least one first tooth comprises a plurality of first teeth, the at least one second tooth comprises a plurality of second teeth, and the plurality of first teeth and the plurality of second teeth are alternately arranged in a circumferential direction.