Bicycle crank assembly

Abstract

Provided is a bicycle crank assembly capable of changing the starting timing of the power stroke of a sprocket. **Solution**: The bicycle crank assembly according to the present invention includes a crank axle rotatably attached to a bicycle frame, and a carrier shaft slidably provided on the crank axle and configured to slide relative to the crank axle in a direction substantially parallel to the center line of the crank axle. This crank assembly also includes an elliptical sprocket attached to the carrier shaft. This elliptical sprocket rotates in response to the rotation of the crank axle to move the bicycle. The starting time of the power stroke of the elliptical sprocket changes by sliding the carrier shaft relative to the crank axle.

Description

Technical Field

[0001] The present invention relates to a bicycle crank assembly, and more particularly, to a bicycle crank assembly having an elliptical sprocket and capable of changing the starting timing of the power stroke of a bicycle.

Background Art

[0002] Conventional bicycles are generally composed of a tubular frame having a rear wheel and a front wheel that can be operated by a handle. The rear wheel is driven by a chain that extends around a sprocket driven by pedals attached to a crank. The sprocket is generally a circular sprocket and starts a pedal stroke (power stroke) when the crank is in an upright position, and the power transmission to the bicycle is not optimal. To overcome this point, the use of elliptical sprockets is increasing. However, an elliptical sprocket cannot exhibit an optimal power stroke when the bicycle is traveling on an inclined ground.

Summary of the Invention

Problems to be Solved by the Invention

[0003] Therefore, a mechanism for maintaining an optimal power stroke of a bicycle is required even when traveling on an inclined ground.

Means for Solving the Problems

[0004] According to one embodiment of the present invention, a bicycle crank assembly is provided. This crank assembly includes a crank axle rotatably attached to the bicycle frame, and a carrier shaft slidably attached to the crank axle and configured to slide relative to the crank axle substantially parallel to the center line of the crank axle. This crank assembly also includes an elliptical sprocket attached to the carrier shaft. This elliptical sprocket rotates in response to the rotation of the crank axle to move the bicycle. The starting timing of the power stroke of the elliptical sprocket changes by sliding the carrier shaft relative to the crank axle.

[0005] In some embodiments, the carrier shaft includes a bent elongated hole formed along the inner surface of the carrier shaft. This carrier shaft rotates about the center line of the crank axle in response to the sliding of the carrier shaft relative to the crank axle, and easily changes the starting timing of the power stroke of the elliptical sprocket.

[0006] In some embodiments, the carrier shaft includes an outer spline provided to engage with the sprocket, thereby coupling the sprocket to the carrier shaft.

[0007] In some embodiments, the crank assembly further includes a lever that engages with the carrier shaft and is operated to enable the sliding of the carrier shaft relative to the crank axle.

[0008] According to one embodiment, the crank assembly further includes a crank arm fixedly attached to the crank axle such that the crank axle rotates easily about the center line of the crank axle.

[0009] In some embodiments, the angular direction of the major axis of the elliptical sprocket with respect to the longitudinal axis of the crank arm changes corresponding to the sliding of the carrier shaft relative to the crank axle.

[0010] In some embodiments, the crank assembly further includes an inclination angle sensor that senses the inclination angle of the ground on which the bicycle is traveling, and the controller is configured to move the lever based on the input from the inclination angle sensor to slide the carrier shaft relative to the crank axle and change the starting timing of the power stroke of the elliptical sprocket.

[0011] According to one embodiment, the controller changes the starting timing of the power stroke of the elliptical sprocket based on the traveling direction of the bicycle.

[0012] In some embodiments, the crank assembly further includes a keeper post for preventing the movement of the sprocket in a direction substantially parallel to the center line of the crank axle.

[0013] According to another embodiment, the following bicycle is disclosed. The bicycle includes a frame, a front wheel and a rear wheel supported by the frame. The bicycle also includes a crank axle rotatably attached to the frame, and a carrier shaft slidably attached to the crank axle and configured to slide relative to the crank axle in a direction substantially parallel to the center line of the crank axle. The bicycle also includes an elliptical sprocket attached to the carrier shaft. The elliptical sprocket rotates in response to the rotation of the crank axle to rotate the rear wheel. The starting timing of the power stroke of the elliptical sprocket is changed by sliding the carrier shaft relative to the crank axle.

[0014] In some embodiments, the carrier shaft includes a curved elongated hole formed along the inner surface of the carrier shaft. The carrier shaft rotates about the center line of the crank axle in response to the sliding of the carrier shaft relative to the crank axle to easily change the starting timing of the power stroke of the elliptical sprocket.

[0015] In some embodiments, the carrier shaft includes an outer surface spline that engages with the sprocket so that the sprocket is securely attached to the carrier shaft.

[0016] In some embodiments, the bicycle further includes a lever that engages with the carrier shaft for operating to slide the carrier shaft relative to the crank axle.

[0017] According to one embodiment, the bicycle further includes a crank arm fixedly attached to the crank axle to facilitate rotation of the crank axle about its center line.

[0018] In some embodiments, the angular direction of the major axis of the elliptical sprocket with respect to the major axis of the crank arm changes in response to sliding of the carrier shaft relative to the crank axle.

[0019] In some embodiments, the bicycle further includes an inclination angle sensor that senses the inclination angle of the ground on which the bicycle travels, and is configured to move the lever based on an input from the inclination angle sensor to slide the carrier shaft relative to the crank axle and change the start timing of the power stroke of the elliptical sprocket.

[0020] According to one embodiment, the controller changes the start time of the power stroke of the elliptical sprocket based on the traveling direction of the bicycle.

[0021] In some embodiments, the bicycle further includes a keeper post for preventing movement of the sprocket in a direction substantially parallel to the center line of the crank axle.

[0022] According to one embodiment, the frame is a split frame having a first tube member and a second tube member, the crank axle is supported by the first tube member and the second tube member, and the carrier shaft is provided at a portion located between the first tube member and the second tube member of the crank axle.

[0023] In some embodiments, the sprocket is disposed between the first tube member and the second tube member.

Advantages of the Invention

[0024] By sliding the carrier shaft relative to the crank axle, the starting timing of the power stroke of the elliptical sprocket can be changed.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0026] Embodiment examples will be described below with reference to the accompanying drawings. Unless explicitly described in the drawings, the sizes, positions, etc. of components, characteristic members, parts, etc., and the distances between them are not necessarily to scale and may be disproportionate and / or exaggerated for clarity.

[0027] The terms used herein are for illustrative purposes only and are not intended to be limiting. As used herein, the singular forms "a", "an" and "the" are to be construed as including the plural forms as well, unless the context clearly dictates otherwise. The terms "comprising", "composed of" and / or "consisting of" as used herein are used to describe the presence of the recited features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Unless otherwise specified, when a range of values is recited, both the upper and lower limits of the range, as well as sub-ranges therebetween, are included. Unless otherwise specified, terms such as "first", "second", etc. are used only to distinguish one element from another. For example, one element can be referred to as the "first element" and similarly another element can be referred to as the "second element". Conversely, this may also be possible. The headings of the terms used herein are for the sole purpose of organizing the text and should not be construed as limiting the described subject matter.

[0028] Unless otherwise specified, terms such as "about", "to that extent", "substantially", etc. mean that the quantity, size, formula, parameter, and other quantities and characteristics are not necessarily exact and may, as appropriate, reflect approximations, and / or larger or smaller values that take into account other factors known to those skilled in the art, such as tolerances, conversion factors, rounding, measurement errors, and the like.

[0029] As shown in the drawings, in order to describe the relationship of one element or feature to another element or feature, spatially relative terms such as "right", "left", "lower", "directly below", "down", "upper", "upper part", etc. may be used in this specification. It is necessary to recognize that spatially relative terms are also intended to encompass various directions in addition to the directions shown in the figures. For example, if an object in the figure is turned over, an element described as "below" or "directly below" another part or object will be "above" the other part or object. Therefore, the term "below" can, for example, encompass both upward and downward directions. The object may be oriented in other directions (for example, rotated 90 degrees or oriented in other directions), and the spatially relative descriptors used here may be interpreted accordingly.

[0030] Unless specifically indicated otherwise, all connections and all operative connections can be either direct or indirect. Similarly, unless specifically indicated otherwise, all connections and all operative connections can be either fixed or non-fixed.

[0031] Throughout, like numbers refer to like elements. Thus, even if not mentioned or described in the corresponding drawings, the same or similar numbers may be referred to and described in other drawings. Also, elements not indicated by reference numbers may be described with reference to other drawings.

[0032] Without departing from the spirit and teachings of the present disclosure, many different forms and embodiments are possible, and thus the present disclosure should not be construed as limited to the exemplary embodiments described herein. Rather, these exemplary embodiments are provided so that the present disclosure will be thorough and complete and will convey the scope of the present disclosure to those skilled in the art.

[0033] References to "one embodiment" or "an embodiment" in this specification mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. When the phrase "in one embodiment" is used in various places in this specification, it does not necessarily refer to the same embodiment, and other embodiments or alternative embodiments are not mutually exclusive of other embodiments.

[0034] Referring to FIG. 1, a bicycle 100 is shown that includes a crank assembly 102 capable of adjusting the timing of the power stroke of pedaling of the bicycle 100 according to the slope of the terrain with respect to the ground and the traveling direction on the slope. The bicycle 100 includes a frame 104, handlebars 106, a front hub assembly 108, a front wheel 110, a rear wheel 112, and a drive unit 116 (having a crank assembly 102 and a rear hub assembly 118).

[0035] The frame 104 includes a frame body 120 and a front fork 122. The frame body 120 includes a top tube 124, a head tube 126, a seat tube 128, a down tube 130, a pair of left and right chain stays 132, a pair of left and right seat stays 134, and a bottom bracket 136 (see FIG. 2). A front fork 122 is rotatably attached to the head tube 126 of the frame body 120, and the handlebars 106 are fixed to the front fork 122.

[0036] The front hub assembly 108 is supported by the front fork 122, and the front wheel 110 is rotatably attached to the front fork 122 via the front hub assembly 108. The rear wheel 112 is rotatably attached to the rear portion of the frame 104 (i.e., the frame body 120) via the rear hub assembly 118.

[0037] Furthermore, the bicycle 100 is provided with a pair of brake levers 140 that are operated by the rider of the bicycle to operate a front brake device and a rear brake device (not shown). Further, the bicycle 100 is provided with a derailleur transmission 144 and a gear change unit 142 attached to the frame 104 (frame body 120). The derailleur transmission 144 moves the bicycle chain 146 from one rear sprocket to an adjacent rear sprocket in response to a shift operation of a shift lever (not shown) attached to the handlebar 106.

[0038] The crank assembly 102 is rotatably supported at the lower part of the frame 104 by, for example, a bottom bracket 136. As best shown in FIG. 2, the crank assembly 102 includes a crank axle 150 (i.e., a pedal shaft 150), a first crank arm 152 (i.e., a right crank arm), a second crank arm (i.e., a left crank arm 154), and a drive sprocket 158 attached to the crank axle 150 and configured to rotate about the center line 160 of the crank axle 150 together with the crank axle 150 when torque / force is applied to the crank arms 152, 154.

[0039] The right crank arm 152 and the left crank arm 154 are attached to both ends of the crank axle 150. For example, the crank axle attachment portion of the left crank arm 154 is fixed to one end of the crank axle 150, and the crank shaft attachment portion of the right crank arm 152 is fixed to the other end of the crank shaft 150. As shown in FIGS. 1 and 2, a first pedal 162 and a second pedal 164 are attached to the pedal attachment portions of the right crank arm 152 and the left crank arm 154, respectively.

[0040] Furthermore, the crank assembly 102 includes a carrier shaft 170 slidably attached to the crank axle 150, and the carrier shaft 170 is provided to slide relative to the crank axle 150 in a direction substantially parallel to the center line 160 of the crank axle 150. The carrier shaft 170 is in the shape of a hollow tube, is disposed between the right crank arm 152 and the frame body 120, and is disposed on the right side of the bicycle 100. As shown in the figure, the carrier shaft 170 has a spline portion 172 formed on the outer surface of the carrier shaft 170 and having a plurality of splines 174 extending radially outward from the outer surface, and a holding structure 176 having a first flange 178 and a second flange 180 extending radially outward from the outer surface of the main body of the carrier shaft 170, with a gap 182 provided between both flanges 178, 180. The spline portion 172 enables engagement of the drive sprocket 158 with the carrier shaft 170, while the holding structure 176 facilitates engagement of the lever 184 of the crank assembly 102 with the carrier shaft 170, enabling the carrier shaft 170 to slide on the crank axle 150 relative to the crank axle 150. The lever 184 is attached to the carrier shaft 170 at a position between the two flanges 178, 180. In one embodiment, the lever 184 is fixedly attached to the carrier shaft 170.

[0041] As shown in FIG. 1, the sprocket 158 is an elliptical sprocket 186 that enables the start of the power stroke of the bicycle 100 when the crank arm, i.e., the right crank arm 152, is in a direction that is neither the upright position nor the lowest position of the crank arm 152. Furthermore, the crank assembly 102 can also shift the start timing of the power stroke of the bicycle 100 by changing the position or angular direction of the major axis 200 of the elliptical sprocket 186 relative to the center line 188 of the right crank arm 152.

[0042] In order to be able to change the starting timing of the power stroke of the bicycle 100 in this way, the carrier shaft 170 includes a long hole 202 extending along the inner surface of the carrier shaft 170. Therefore, the long hole 202 is not on a straight line substantially parallel to / parallel with the center line 160 of the carrier shaft 170, but moves in an arc around the center line 160 along the inner surface of the carrier shaft 170 and linearly extends in the direction of the center line 160. Therefore, the projection of the slot 202 in the horizontal plane including the center line 160 is inclined with respect to the center line 160 and intersects the center line 160 when viewed from above. Also, the carrier shaft 170 engages with the crank axle 150 by inserting a radial projection or key 204 of the crank axle 150 into the slot 202. Therefore, when the carrier shaft 170 is slid along the center line 160 using the lever 184, the carrier shaft 170 also rotates around the center line 160, and the angular position of the crank arm, for example, the right crank arm 152, changes with respect to the major axis 200 of the sprocket 158, and the starting timing of the power stroke of the bicycle 100 (that is, the elliptical sprocket 186) changes. In this way, by sliding the carrier shaft 170 in the first direction or the second direction opposite to the first direction, the starting timing of the power stroke can be advanced or delayed.

[0043] Further, or alternatively, the bicycle 100 may include an actuator (not shown), such as an electric motor, that operates / moves the lever 184 to slide the carrier shaft 170 on the crank axle 150 to change the starting timing of the power stroke of the bicycle 100. To do this, the bicycle 100 (i.e., the crank assembly 102) may include a controller 210 operably connected to the actuator to operate the actuator. In one embodiment, the bicycle 100 (i.e., the crank assembly 102) may include an inclination angle sensor 212 that senses the inclination angle of the terrain on which the bicycle 100 is traveling, and a direction sensor 214 that determines whether the bicycle 100 is traveling uphill or downhill. The controller actuates the actuator based on the inputs received from the sensors 212, 214 to operate the lever and appropriately slide and position the carrier shaft 170 to adjust the starting timing of the power stroke of the bicycle. In some embodiments, instead of the sensors 212, 214, the rider of the bicycle operates the actuator to operate the lever 184 and operates a switch (not shown) to slide the carrier shaft 170 on the crank axle 150. In one embodiment, the rider of the bicycle can operate the switch in a first direction to advance the starting timing of the power stroke and operate the switch in a second direction to delay the starting timing of the power stroke. In some embodiments, the rider of the bicycle can manually operate the lever 184 to adjust the starting time of the power stroke of the bicycle (i.e., the elliptical sprocket 186).

[0044] In an exemplary scenario, as shown in FIG. 3, when the bicycle 100 is moving on a horizontal ground, considering one rotation of the right crank arm 152 as the rotation of the hands of a clock face, the power stroke of the bicycle 100 starts when the center line 188 of the right crank arm 152 is at the position of "2" on the clock face. Therefore, the starting timing of the power stroke corresponds to when the right crank arm 152 is at an angle of 60 degrees from the upright position. During the uphill or downhill movement of the bicycle 100, it is desirable to change the starting timing of the power stroke of the bicycle 100 so as to maintain an appropriate power exertion region against gravity regardless of the change in the posture of the bicycle frame 104 (i.e., the frame body 120).

[0045] Therefore, the controller 210 can adjust the starting timing of the power stroke of the bicycle 100 during uphill or downhill travel according to the slope of the road and the direction of travel (uphill or downhill). To do this, when the bicycle 100 is traveling uphill, the controller 210 operates the lever 184 to slide the carrier shaft 170 relative to the crank axle 150, delaying the starting timing of the power stroke, so that the power stroke can be started later compared to when the bicycle 100 is moving on a substantially horizontal road. Therefore, in the example shown in FIG. 3, when the carrier shaft 170 moves on the crank axle 150 and the right crank arm 152 is positioned at the position corresponding to "3" on the clock face, that is, when the right crank arm 152 forms a 90-degree angle with respect to the upright position when going uphill, the power stroke is started. Similarly, when the bicycle 100 is traveling downhill, the controller 210 operates the lever 184 to slide the carrier shaft 170 relative to the crank axle 150, so that the power stroke can be started earlier than the starting time of the power stroke when the bicycle 100 is traveling on a substantially horizontal road. Therefore, in the example shown in FIG. 3, when the carrier shaft 170 moves on the crank axle 150 and is positioned / arranged / located at the position corresponding to "1" on the clock face when traveling downhill, that is, when the right crank arm forms a 30-degree angle with respect to the upright position, the power stroke is started. Therefore, the crank assembly 102 of the bicycle 100 helps to maintain an appropriate power exertion area against gravity regardless of the change in the posture of the bicycle frame 104 (i.e., the frame body 120).

[0046] Furthermore, the bicycle 100 may include a keeper post 220 (shown in FIG. 2) attached to the frame body 120 of the bicycle 100 and extending in a direction substantially parallel to the crank axle 150. The keeper post 220 is configured to prevent the sprocket 158 from moving substantially parallel to the center line 160 of the crank axle 150 when the carrier shaft 170 moves on the crank axle 150, and at the same time, to facilitate the rotation of the sprocket 158 about its rotation axis (the center line 160 of the crank axle 150). Thus, when the carrier shaft 170 is linearly moved relative to the crank axle 150, the distance between the sprocket 158 and the frame body 120 remains constant in the direction of the center line 160. In one embodiment, the keeper post 220 may include a wear ring (not shown) that supports the sprocket 158. Further, the diameter of the crank axle 150 may be varied along the center line 160 of the crank axle 150 to appropriately distribute the weight on the bearing that supports the crank axle 150. In one embodiment, the diameter of the crank axle 150 decreases from the bottom bracket 136 toward the right crank arm 152.

[0047] FIG. 4 shows a part of the bicycle 100' according to the modified embodiment. The bicycle 100' is similar to the bicycle 100, but the down tube 130' is a split tube having a first tube member 138' and a second tube member 139' which are spaced apart from each other and have a space 141' therebetween. Accordingly, the first portion (the right portion in the figure) of the crank axle 150 is rotatably supported by the first tube member 138', and the second portion (the left portion in the figure) of the crank axle 150 is rotatably supported by the second tube member 139'. Further, the sprocket 158, the carrier shaft 170, and the lever 184 are disposed in the space 141' and are supported by the central portion of the crank axle 150 located in the space. Further, the key keeper post 220' extends into the space 141' and extends substantially parallel to the center line 160 of the crank axle 150 from the second tube member 139' toward the first tube member 138'. The structure and function of the key keeper post 220' are the same as those of the key keeper post 220 of the bicycle 100.

[0048] Regarding the disclosures described herein, those skilled in the art of the related art of these disclosures will envision many modifications and other embodiments by virtue of the foregoing description and the teachings shown in the related drawings. Accordingly, it is to be understood that the disclosures herein are not to be limited to the specific embodiments shown herein, but are intended to include modifications and other embodiments within the scope of the claims. Further, the foregoing description and the related drawings illustrate exemplary embodiments in the context of specific exemplary combinations of components and / or functions, but it is to be understood that alternative embodiments may also provide different combinations of components and / or functions without departing from the scope of the appended claims.

Description of Reference Numerals

[0049] 100 Bicycle 102 Crank assembly 104 Frame 106 Handlebar 108 Front hub assembly 110 Front wheel 112 Rear wheel 116 Driving part 118 Rear hub assembly 120 Frame body 122 Front fork 124 Top tube 126 Head tube 128 Seat tube 130 Down tube 132 Pair of chain stays 134 Pair of seat stays 136 Bottom bracket 140 Pair of brake levers 144 Derailleur gearshift 142 Gear change part 146 Bicycle chain 150 Crank axle (pedal shaft) 152 Right crank arm 154 Left crank arm 158 Driving sprocket 160 Center line of crank axle 170 Carrier shaft 172 Spline part 174 Multiple splines 176 Holding structure 178, 180 Flange 182 Gap 184 Lever 186 Elliptical sprocket 188 Center line of right crank arm 200 Major axis of elliptical sprocket 210 Controller 212 Tilt angle sensor 214 Direction sensor 220 Keypost

Claims

1. A crank axle rotatably attached to a bicycle frame, a carrier shaft slidably attached to the crank axle and configured to slide relative to the crank axle substantially parallel to the center line of the crank axle, and an elliptical sprocket attached to the carrier shaft, the elliptical sprocket rotating in response to rotation of the crank axle to move the bicycle, and a starting time of a power stroke of the elliptical sprocket being changed by sliding the carrier shaft relative to the crank axle. A crank assembly for a bicycle, characterized in that.

2. The carrier shaft includes a bent elongated hole formed along an inner surface of the carrier shaft, and the carrier shaft rotates about the center line of the crank axle in response to sliding of the carrier shaft relative to the crank axle, and the power stroke of the elliptical sprocket The crank assembly for a bicycle according to claim 1, wherein the start time of is easily changed.

3. The crank assembly for a bicycle according to claim 1, wherein the carrier shaft includes an outer surface spline provided to engage with the sprocket, thereby coupling the sprocket to the carrier shaft.

4. The crank assembly for a bicycle according to claim 1, further comprising a lever that engages with the carrier shaft and is operated to enable sliding of the carrier shaft relative to the crank axle.

5. The crank assembly for a bicycle according to claim 1, further comprising a crank arm fixedly attached to the crank axle so that the crank axle rotates easily about the center line of the crank axle.

6. The crank assembly for a bicycle according to claim 1, wherein an angular direction of a major axis of the elliptical sprocket with respect to a longitudinal axis of the crank arm changes in response to sliding of the carrier shaft relative to the crank axle.

7. Further comprising an inclination angle sensor for sensing the inclination angle of the ground on which the bicycle is traveling, the controller is configured to move the lever based on the input from the inclination angle sensor to slide the carrier shaft relative to the crank axle and change the starting timing of the power stroke of the elliptical sprocket. The crank assembly for a bicycle according to claim 1.

8. The controller is configured to change the starting timing of the power stroke of the elliptical sprocket based on the traveling direction of the bicycle. The crank assembly for a bicycle according to claim 7.

9. Further comprising a keeper post for preventing the movement of the sprocket in a direction substantially parallel to the center line of the crank axle. The crank assembly for a bicycle according to claim 1.

10. A frame, a front wheel and a rear wheel supported by the frame, a crank axle rotatably attached to the frame, a carrier shaft slidably attached to the crank axle and configured to slide relative to the crank axle in a direction substantially parallel to the center line of the crank axle, and an elliptical sprocket attached to the carrier shaft. The elliptical sprocket rotates in response to the rotation of the crank axle to rotate the rear wheel, and the starting timing of the power stroke of the elliptical sprocket is changed by sliding the carrier shaft relative to the crank axle. A bicycle characterized by this.

11. The carrier shaft includes a bent elongated hole formed along the inner surface of the carrier shaft, and the carrier shaft rotates about the center line of the crank axle in response to the sliding of the carrier shaft relative to the crank axle to easily change the starting timing of the power stroke of the elliptical sprocket. The bicycle according to claim 10.

12. The carrier shaft includes an outer spline engaged with the sprocket so that the sprocket is securely attached to the carrier shaft. The bicycle according to claim 11.

13. Further comprising a lever engaged with the carrier shaft for operating to slide the carrier shaft relative to the crank axle. The bicycle according to claim 11.

14. The bicycle according to claim 11, further comprising a crank arm fixedly attached to the crank axle to facilitate rotation of the crank axle about its center line.

15. The bicycle according to claim 14, wherein an angular direction of the major axis of the elliptical sprocket with respect to the longitudinal axis of the crank arm varies in correspondence with a slide of the carrier shaft with respect to the crank axle.

16. The bicycle according to claim 11, further comprising an inclination angle sensor configured to sense an inclination angle of a ground on which the bicycle travels, wherein a controller is configured to move a lever based on an input from the inclination angle sensor to slide the carrier shaft with respect to the crank axle and change a start timing of a power stroke of the elliptical sprocket.

17. The bicycle according to claim 16, wherein the controller changes a start time of a power stroke of the elliptical sprocket based on a traveling direction of the bicycle.

18. The bicycle according to claim 11, further comprising a keeper post configured to prevent movement of the sprocket in a direction substantially parallel to a center line of the crank axle.

19. The bicycle according to claim 11, wherein the frame is a split frame having a first tube member and a second tube member, the crank axle is supported by the first tube member and the second tube member, and the carrier shaft is provided at a portion located between the first tube member and the second tube member of the crank axle.

20. The bicycle according to claim 19, wherein the sprocket is disposed between the first tube member and the second tube member.

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