Bicycle crank assembly

Abstract

A bicycle crank assembly includes a rotatable crankshaft mounted on a frame of a bicycle, and a slidable carrier shaft mounted on the crankshaft, the carrier shaft being arranged to slide relative to the crankshaft in a direction substantially parallel to a central longitudinal axis of the crankshaft. The crank assembly also includes an elliptical sprocket mounted on the carrier shaft. And the elliptical chain wheel rotates along with the rotation of the crankshaft, so that the bicycle advances. The start time of the elliptical sprocket power stroke is varied by the sliding of the carrier shaft relative to the crankshaft.

Description

Technical Field

[0001] The present invention generally relates to a bicycle crank assembly, and more particularly to a bicycle crank assembly having an elliptical sprocket and capable of changing the start time of a bicycle power stroke. Background Art

[0002] A conventional bicycle comprises a generally tubular frame having a front wheel steerable by handlebars and a rear wheel. The rear wheel is driven by a chain extending around a sprocket which is driven by pedals mounted on cranks. The sprockets are generally round sprockets and the pedal stroke begins when the cranks are in a vertical upward position, which does not provide optimal power transmission for the bicycle. To overcome this problem, oval sprockets or elliptical sprockets are increasingly being used. However, the power stroke of oval sprockets or elliptical sprockets is less than optimal when the bicycle is driven on inclined terrain. Therefore, there is a need for a mechanism that maintains the optimal power stroke of the bicycle even when the bicycle is driven on inclined terrain. Summary of the invention

[0003] According to one embodiment of a bicycle crank assembly, the crank assembly includes a crank shaft rotatably mounted on a bicycle frame, and a bearing shaft slidably mounted on the crank shaft, the bearing shaft being configured to slide relative to the crank shaft in a direction substantially parallel to a central longitudinal axis of the crank shaft. The crank assembly also includes an elliptical sprocket mounted on the bearing shaft. The elliptical sprocket rotates with the rotation of the crank shaft to enable the bicycle to travel. The start time of the power stroke of the elliptical sprocket is changed by the sliding of the bearing shaft relative to the crank shaft.

[0004] In some embodiments, the bearing shaft includes a groove curved along the inner surface of the bearing shaft. The bearing shaft rotates around the central longitudinal axis as the bearing shaft slides relative to the crankshaft, thereby changing the start time of the elliptical sprocket power stroke.

[0005] In some embodiments, the carrier shaft includes external splines adapted to engage the sprocket to couple the sprocket to the carrier shaft.

[0006] In some embodiments, the crank assembly further comprises a lever engaged with the load-bearing shaft, and the load-bearing shaft can be slidably moved relative to the crank shaft by operating the lever.

[0007] According to one embodiment, the crank assembly further comprises a crank arm fixedly attached to the crank axle, the crank arm enabling the crank axle to rotate around a central longitudinal axis of the crank axle.

[0008] In some embodiments, the angle between the major axis of the elliptical sprocket and the longitudinal axis of the crank arm changes as the carrier shaft slides relative to the crank shaft.

[0009] In some embodiments, the crank assembly further comprises an inclination sensor for determining an inclination angle of terrain on which the bicycle is travelling and a controller, wherein the controller is configured to cause a lever movement based on input from the inclination sensor to slide the load-bearing shaft relative to the crank shaft, thereby changing the start time of the elliptical sprocket power stroke.

[0010] According to one embodiment, the controller varies the start time of the elliptical sprocket power stroke based on the direction the bicycle is traveling.

[0011] In some embodiments, the crank assembly further includes a retainer post to prevent the sprocket from moving in a direction substantially parallel to the central longitudinal axis.

[0012] According to another exemplary bicycle embodiment, the bicycle includes a frame, a front wheel and a rear wheel supported on the frame. The bicycle also includes a crankshaft rotatably mounted on the frame, and a bearing shaft slidably mounted on the crankshaft, wherein the bearing shaft is configured to slide relative to the crankshaft in a direction substantially parallel to a central longitudinal axis of the crankshaft. The bicycle also includes an elliptical sprocket mounted on the bearing shaft. The elliptical sprocket rotates with the rotation of the crankshaft to rotate the rear wheel. The start time of the power stroke of the elliptical sprocket is changed by the sliding of the bearing shaft relative to the crankshaft.

[0013] In some embodiments, the bearing shaft includes a groove curved along the inner surface of the bearing shaft. The bearing shaft rotates around the central longitudinal axis as the bearing shaft slides relative to the crankshaft, thereby changing the start time of the elliptical sprocket power stroke.

[0014] In some embodiments, the carrier shaft includes external splines adapted to engage with the sprocket to securely mount the sprocket on the carrier shaft.

[0015] In some embodiments, the bicycle further comprises a lever engaged with the load-bearing shaft, and the load-bearing shaft can slide relative to the crank shaft by operating the lever.

[0016] According to one embodiment, the bicycle further comprises a crank arm fixedly attached to the crank axle, wherein the crank arm enables the crank axle to rotate around a central longitudinal axis of the crank axle.

[0017] In some embodiments, the angle between the major axis of the elliptical sprocket and the longitudinal axis of the crank arm changes as the carrier shaft slides relative to the crank shaft.

[0018] In some embodiments, the bicycle further comprises an inclination sensor for determining an inclination angle of terrain on which the bicycle is travelling and a controller, the controller being configured to cause a lever movement based on input from the inclination sensor to slide the carrier shaft relative to the crank shaft, thereby changing a start time of a power stroke of the elliptical sprocket.

[0019] According to an embodiment, the controller changes the start time of the power stroke of the elliptical sprocket according to a traveling direction of the bicycle.

[0020] In some embodiments, the bicycle further includes a retainer post to prevent the sprocket from moving in a direction substantially parallel to the central longitudinal axis.

[0021] According to an embodiment, the frame is a split frame having a first tube and a second tube. The crankshaft is supported on the first tube and the second tube, and the bearing shaft is installed on a portion of the crankshaft between the first tube and the second tube.

[0022] In some embodiments, the sprocket is disposed between the first tube and the second tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A side view of an example of a bicycle according to an embodiment of the present invention;

[0024] Figure 2 According to the embodiment of the present invention Figure 1 A schematic diagram of a bicycle crank assembly;

[0025] Figure 3 is a timing diagram according to an embodiment of the present invention, the timing diagram describing a power stroke of a bicycle;

[0026] Figure 4 Schematic diagram of a crank assembly mounted on a bicycle according to an alternative embodiment of the present invention. DETAILED DESCRIPTION

[0027] Exemplary embodiments are described below with reference to the accompanying drawings. Unless otherwise explicitly stated in the drawings, the sizes, positions, etc. of components, features, elements, etc. and any distances therebetween are not necessarily drawn to scale and may be disproportionately and / or exaggeratedly enlarged for clarity.

[0028] The terms used herein are only used to describe specific exemplary embodiments and are not restrictive. As used herein, the indefinite article "one" and the definite article "said" in the singular form also include plural forms, unless the context clearly states otherwise. It should be understood that the verb term "include" used in this specification to represent the plural meaning, the verb term "include" to represent the singular meaning and / or the adjectival verb "include" represent the existence of the features, integers, steps, operations, elements and / or elements, but do not exclude the existence or addition of one or more other features, integers, steps, operations, elements, elements and / or their combinations. Unless otherwise specified, when a numerical range is listed, the upper and lower limits of the range are included, as well as any sub-ranges between the two. Unless otherwise specified, terms such as "first", "second" and the like are only used to distinguish one element from another element. For example, an element may be referred to as a "first element", and similarly, another element may be referred to as a "second element", and vice versa. The section titles used herein are only used to present the section architecture and should not be understood as restrictive interpretations made to the subject matter.

[0029] Unless otherwise indicated, terms such as “about,” “approximately,” and “substantially” indicate that quantities, sizes, formulations, parameters, and other quantities and features are not and need not be exact, but may be approximate and / or larger or smaller, reflecting tolerances, conversion factors, rounding, measurement errors, etc., as necessary, and other factors known to those skilled in the art.

[0030] For ease of description, this document may use terms that describe spatial relative concepts, such as "right", "left", "lower", "lower", "upper", and "upper", etc., to describe the relationship between one element or feature and another element or feature, as shown in the figure. It should be understood that in addition to the directions described in the figure, the description of spatial relative concepts also covers other directions. For example, if an object in the figure is turned over, the element described as being "below" or "below" other elements or features will be turned over to be "above" other elements or features. Therefore, a term such as "below" can include both the above and below directions. The object may also be oriented in other ways (for example: rotated 90 degrees or in other directions), and the terms used in this document to describe spatial relative concepts can be understood accordingly.

[0031] Unless otherwise expressly stated, all connections and all operable connections may be direct or indirect. Likewise, unless otherwise expressly stated, all connections and all operable connections may be rigid or non-rigid.

[0032] Like numbers refer to like elements throughout the text. Therefore, the description of the same or similar numbers can refer to the annotations of other drawings, even if they are neither mentioned nor labeled in the corresponding drawings. In addition, even if the elements are not marked with reference numbers, they can also be labeled with reference to other drawings.

[0033] Without departing from the spirit and enlightenment of the present invention, there may be a variety of different forms and embodiments, so the present invention should not be interpreted as being limited to the exemplary embodiments described herein. On the contrary, these exemplary embodiments are provided to make the content disclosed by the present invention comprehensive and complete, and to make those skilled in the art aware of the scope of the present invention.

[0034] The "one embodiment" or "an embodiment" mentioned in this specification means that the specific features, structures or characteristics related to the embodiment are included in at least one embodiment disclosed in the present invention. The term "in one embodiment" appearing in various places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or alternative embodiment other than other embodiments.

[0035] like Figure 1 A bicycle 100 having a crank assembly 102 is shown, wherein the crank assembly can adjust the timing of the pedaling power stroke of the bicycle 100 according to the terrain inclination relative to the ground and the direction of travel on the inclined terrain. The bicycle 100 includes a frame 104, a handlebar 106, a front hub assembly 108, a front wheel 110, a rear wheel 112, and a drive part 116 (including the crank assembly 102 and the rear hub assembly 118).

[0036] 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 chain stays 132, a pair of seat stays 134, and a bottom bracket 136 (see FIG. Figure 2 The front fork 122 is rotatably attached to the head tube 126 of the frame body 120 , and the handlebar 106 is fixed to the front fork 122 .

[0037] The front hub assembly 108 is supported on the front fork 122, and the front wheel 110 is rotatably attached to the front fork 122 through the front hub assembly 108. The rear wheel 112 is rotatably attached to the rear of the frame 104 (ie, the frame body 120) through the rear hub assembly 118.

[0038] Further, the bicycle 100 includes a pair of brake levers 140 that can be manipulated by a bicycle rider to apply front and rear brake devices (not shown) of the bicycle 100. Further, the bicycle 100 includes a shifting portion 142 that has a derailleur 144 and is attached to the frame 104 (frame body 120). When a shifting lever (not shown) attached to the handlebar 106 performs a shifting operation, the derailleur 144 moves a bicycle chain 146 from a rear sprocket of one gear to a rear sprocket of an adjacent other gear.

[0039] The crank assembly 102 is rotatably supported at the lower portion of the frame 104, for example, by a bottom bracket 136. Figure 2 As best shown, the crank assembly 102 includes a crank axle 150 (i.e., pedal axle 150), a first crank arm 152 (i.e., right crank arm), a second crank arm (i.e., left crank arm 154), and a drive sprocket 158 ​​mounted on the crank axle 150, which is configured to rotate with the crank axle 150 around a central longitudinal axis 160 of the crank axle 150 when torque / force is applied to the crank arms 152, 154.

[0040] The right crank arm 152 and the left crank arm 154 are mounted on opposite ends of the crank axle 150. For example, the crank axle mounting portion of the left crank arm 154 is fixedly attached to one end of the crank axle 150, and the crank axle mounting portion of the right crank arm 152 is fixedly attached to the other end of the crank axle 150. Figure 1 and Figure 2 As shown, a first pedal 162 and a second pedal 164 are attached to the pedal mounting portions of the right crank arm 152 and the left crank arm 154 .

[0041] In addition, the crank assembly 102 includes a bearing shaft 170 slidably mounted on the crank shaft 150, and the bearing shaft can slide relative to the crank shaft 150 in a direction substantially parallel to the central longitudinal axis 160 of the crank shaft 150. The bearing shaft 170 is in the form of a hollow tube, and is disposed between the right crank arm 152 and the frame body 120, and is located on the right side of the bicycle 100. As shown in the figure, the bearing shaft 170 includes a spline portion 172 having a plurality of splines 174 and a retaining structure 176, wherein the splines are arranged on the outer surface of the bearing shaft 170 and protrude outwardly in the radial direction of the outer surface, and the retaining structure 176 has a first flange 178 and a second flange 180, wherein the first and second flanges protrude outwardly in the radial direction of the outer surface of the main body of the bearing shaft 170 and maintain a gap 182 with each other. The spline portion 172 engages the drive sprocket 158 ​​to the carrier shaft 170, and the retaining structure 176 engages the lever 184 of the crank assembly 102 to the carrier shaft 170 to slide the carrier shaft 170 on the crank shaft 150 relative to the crank shaft 150. The lever 184 is mounted on the carrier shaft 170 between the two flanges 178 and 180. In one embodiment, the lever 184 is fixedly attached / mounted to the carrier shaft 170.

[0042] like Figure 1 As shown, the sprocket 158 ​​is an elliptical sprocket 186, which can start the power stroke of the bicycle 100 when the crank arm (i.e., the right crank arm 152) is not at the top position and the bottom position of the crank arm 152. In addition, the crank assembly 102 can also change the start time of the power stroke of the bicycle 100 by changing the relative position or angle between the main axis 200 of the elliptical sprocket 186 and the longitudinal axis 188 of the right crank arm 152.

[0043] To achieve this change in the start time of the power stroke of the bicycle 100, the bearing shaft 170 includes a groove 202 extending in a curved manner along the inner surface of the bearing shaft 170. Therefore, the groove 202 is not on a straight line substantially parallel to / aligned with the central longitudinal axis 160 of the bearing shaft 170, but the groove 202 is along the inner surface of the bearing shaft 170 around the central longitudinal axis 160 in an arc motion trajectory and extends linearly in the direction of the axis 160. Therefore, when viewed from a top view, the projection of the groove 202 on a plane containing the central longitudinal axis 160 is inclined to and intersects the central longitudinal axis 160. In addition, the bearing shaft 170 is engaged with the crank shaft 150 by inserting a radial protrusion or key 204 of the crank shaft 150 into the groove 202. Therefore, when the bearing shaft 170 slides along the central longitudinal axis 160 by using the lever 184, the bearing shaft 170 also rotates about the central longitudinal axis 160, thereby causing the angular position of the crank arm (e.g., the right crank arm 152) relative to the main axis 200 of the sprocket 158 ​​to change, thereby changing the start time of the power stroke of the bicycle 100 (i.e., the elliptical sprocket 186). In this way, by sliding the bearing shaft 170 in a first direction or a second direction opposite to the first direction, the start time of the power stroke can be advanced or delayed.

[0044] The bicycle 100 may additionally or selectively include an actuator (not shown), such as an electric motor for operating / moving the lever 184, through which the bearing shaft 170 slides on the crank shaft 150, thereby changing the start time of the power stroke of the bicycle 100. To this end, the bicycle 100 (i.e., the crank assembly 102) may include a controller 210 that is functionally connected to the actuator to operate the actuator. In one embodiment, the bicycle 100 (i.e., the crank assembly 102) may include an inclination sensor 212 for determining the inclination angle of the terrain on which the moving bicycle 100 is located, and a direction sensor 214 for determining whether the bicycle 100 is traveling uphill or downhill. Based on the input received from the sensors 212, 214, the controller can activate the actuator to operate the lever to slide appropriately and position the bearing shaft 170 to adjust the start time of the bicycle power stroke. In some embodiments, the rider can operate a switch (not shown) instead of the sensors 212, 214 to move the actuator to operate the lever 184, thereby sliding the carrier shaft 170 on the crank shaft 150. In one embodiment, the rider of the bicycle can operate the switch in a first direction to advance the start time of the power stroke, and can operate the switch in a second direction to delay the start time of the power stroke. In some embodiments, the rider can manually manipulate the lever to adjust the start time of the power stroke of the bicycle (i.e., the elliptical sprocket 186).

[0045] In an exemplary scenario, Figure 3As shown, one full rotation of the right crank arm 152 is considered as a clock face, and during the movement of the bicycle 100 on the horizontal ground, when the central axis 188 of the right crank arm 152 is located at 2, the power stroke of the bicycle 100 begins. Therefore, the start time of the power stroke corresponds to when the right crank arm 152 rotates from the vertical upward position to the position at a 60-degree angle. During the uphill or downhill movement of the bicycle 100, it is preferable to change the start time of the power stroke of the bicycle 100 to maintain a proper power zone position relative to gravity without being affected by the change in the posture of the bicycle frame 104 (i.e., the frame body 120).

[0046] Thus, the controller 210 can adjust the start time of the power stroke of the bicycle 100 during uphill and downhill movement depending on the inclination of the road and the direction of travel (i.e., uphill or downhill movement). To this end, during uphill movement of the bicycle 100, the controller 210 can operate the lever 184 and slide the load-bearing shaft 170 relative to the crankshaft 150 to delay the start time of the power stroke so that the start time of the power stroke is later than the start time of the power stroke when the bicycle 100 is moving on a substantially horizontal path. Thus, in the illustrated example, as Figure 3 As shown, the bearing shaft 170 moves on the crank shaft 150 so that the power stroke begins when the right crank arm 152 is at a position corresponding to 3 on the clock face, that is, when the right crank arm 152 is at a 90-degree angle relative to the vertical upward position when going uphill. Similarly, during downhill movement of the bicycle 100, the controller 210 can operate the lever 184 and slide the bearing shaft 170 relative to the crank shaft 150 to advance the start time of the power stroke and earlier than the start time of the power stroke when the bicycle 100 moves on a substantially horizontal path. Therefore, in the illustrated example, as Figure 3 As shown, the bearing shaft 170 moves on the crank shaft 150 so that the power stroke begins when the right crank arm 152 is positioned / arranged / located at the position corresponding to 1 on the clock face, that is, when the right crank arm is at a 30-degree angle relative to the vertical upward position when going downhill. Therefore, the crank assembly 102 of the bicycle 100 is convenient to maintain an appropriate power zone position relative to gravity without being affected by changes in the posture of the bicycle frame 104 (i.e., the frame body 120).

[0047] In addition, the bicycle 100 may include a retainer post 220 (eg, a retainer post 220) attached to the frame body 120 of the bicycle 100 and extending in a direction substantially parallel to the crank axle 150. Figure 2160 ). The retainer post 220 is configured to prevent the sprocket 158 ​​from moving in a direction substantially parallel to the central longitudinal axis 160 when the carrier shaft 170 moves on the crank axle 150, while promoting the sprocket 158 ​​to rotate about its central longitudinal axis 160. In this way, when the carrier shaft 170 moves linearly relative to the crank axle 150, the distance between the sprocket 158 ​​and the frame body 120 remains constant in the direction of the central longitudinal axis 160. In one embodiment, the retainer post 220 may include a wear ring (not shown) that supports the sprocket 158. In addition, in order to manage the weight distribution on the bearings used to support the crank axle 150, the diameter of the crank axle 150 can vary along the central longitudinal axis 160 of the crank axle 150. In one embodiment, the diameter of the crank axle 150 decreases in a direction from the bottom bracket 136 toward the right crank arm 152.

[0048] Figure 4 A portion of a bicycle 100' according to an alternative embodiment is shown. Bicycle 100' is similar to bicycle 100, except that down tube 130' is a split tube having a first tube 138' and a second tube 139', which are spaced apart from each other and form a space 141' therebetween. Thus, a first portion of crank axle 150 is supported and rotatable by first tube 138', and a second portion of crank axle 150 is supported and rotatable by second tube 139'. Further, sprocket 158, bearing shaft 170, and lever 184 are disposed within space 141' and supported on the portion of crank axle 150 disposed within space. In addition, retainer post 220' extends within space 141' and extends from second tube 139' to first tube 138' in a direction substantially parallel to central longitudinal axis 160 of crank axle 150. The structure and function of the retainer post 220 ′ are similar to the retainer post 220 of the bicycle 100 .

[0049] With the benefit of the teachings presented in connection with the present specification and the accompanying drawings, those skilled in the art will appreciate many modifications and other embodiments of the present invention. Therefore, it should be understood that the disclosure is not limited to the specific embodiments disclosed, and modifications and other embodiments should be included within the scope of the appended claims. In addition, although the above description and the accompanying drawings describe exemplary embodiments for certain exemplary combinations of elements and / or functions, it should be understood that different combinations of elements and / or functions may be provided by other embodiments without departing from the scope of the appended claims.

Claims

1. A bicycle crank assembly, the crank assembly comprising: A crank shaft rotatably mounted on a bicycle frame; a bearing shaft slidably mounted on the crank shaft, the bearing shaft being configured to slide relative to the crank shaft in a direction substantially parallel to a central longitudinal axis of the crank shaft; and An elliptical sprocket mounted on the carrier shaft rotates with the rotation of the crankshaft to move the bicycle forward. The start time of the elliptical sprocket power stroke is changed by sliding the load-bearing shaft relative to the crankshaft.

2. The crank assembly according to claim 1, wherein the bearing shaft comprises a groove curved along the inner surface of the bearing shaft, wherein: The carrier shaft rotates about the central longitudinal axis as the carrier shaft slides relative to the crank shaft, thereby changing the start time of the elliptical sprocket power stroke.

3. The crank assembly of claim 1, wherein the carrier shaft includes external splines that mesh with the sprocket to connect the sprocket to the carrier shaft.

4. The crank assembly according to claim 1 further comprises a lever engaged with the load-bearing shaft, and the load-bearing shaft can slide relative to the crank shaft by operating the lever.

5. The crank assembly of claim 1, further comprising a crank arm fixedly attached to the crank axle, the crank arm enabling the crank axle to rotate about a central longitudinal axis of the crank axle.

6. The crank assembly of claim 5, wherein the angle between the main axis of the elliptical sprocket and the longitudinal axis of the crank arm changes as the load-bearing shaft slides relative to the crank shaft.

7. The crank assembly according to claim 1, further comprising An inclination sensor and controller for determining the inclination angle of the terrain on which the bicycle is traveling, and The controller is configured to cause movement of the lever based on input from the inclination sensor to slide the carrier shaft relative to the crank shaft, thereby changing the start time of the elliptical sprocket power stroke.

8. The crank assembly of claim 7, wherein the controller varies the timing of the start of the elliptical sprocket power stroke based on the direction of travel of the bicycle.

9. The crank assembly of claim 1 further comprising a retainer post to prevent the sprocket from moving in a direction substantially parallel to the central longitudinal axis.

10. A bicycle comprising: frame; front and rear wheels supported on the frame; A crank shaft rotatably mounted on the frame; a carrier shaft slidably mounted on the crank shaft and configured to slide relative to the crank shaft in a direction substantially parallel to a central longitudinal axis of the crank shaft; and an elliptical sprocket mounted on the bearing shaft, wherein the elliptical sprocket rotates with the rotation of the crankshaft to rotate the rear wheel, The starting time of the power stroke of the elliptical sprocket is changed by the sliding of the load-bearing shaft relative to the crankshaft.

11. The bicycle according to claim 10, wherein the load-bearing shaft includes a groove curved along the inner surface of the load-bearing shaft, wherein: The carrier shaft rotates about the central longitudinal axis as the carrier shaft slides relative to the crank shaft, thereby changing the start time of the power stroke of the elliptical sprocket.

12. The bicycle of claim 11, wherein the carrier shaft includes external splines that engage the sprocket to securely mount the sprocket on the carrier shaft.

13. The bicycle according to claim 11, further comprising a lever engaged with the load-bearing shaft, wherein the load-bearing shaft can slide relative to the crank shaft by operating the lever.

14. The bicycle of claim 11, further comprising a crank arm fixedly attached to the crank axle, the crank arm enabling the crank axle to rotate about a central longitudinal axis of the crank axle.

15. The bicycle of claim 14, wherein the angle between the major axis of the elliptical sprocket and the longitudinal axis of the crank arm changes as the load-bearing shaft slides relative to the crank shaft.

16. The bicycle of claim 11, further comprising: An inclination sensor and controller for determining the inclination angle of the terrain on which the bicycle is traveling, and The controller is configured to cause movement of the lever based on input from the inclination sensor to slide the carrier shaft relative to the crank shaft, thereby changing the start time of the elliptical sprocket power stroke.

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

18. The bicycle of claim 11, further comprising a retainer post to prevent the sprocket from moving in a direction substantially parallel to the central longitudinal axis.

19. The bicycle according to claim 11, wherein the frame is a split frame having a first tube and a second tube, wherein: The crankshaft is supported on the first tubular member and the second tubular member, and the bearing shaft is installed on a portion of the crankshaft between the first tubular member and the second tubular member.

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

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