Bicycle chain drive mechanism

Abstract

To enable a known external transmission to be selectively used in a bicycle chain drive mechanism that can transmit driving force to a rear wheel even when the rotation direction of a crankshaft is either a forward direction or a reverse direction.SOLUTION: A bicycle chain drive mechanism includes: a main freewheel 14 configured to rotate coaxially with a crankshaft 12 of a bicycle and transmit torque acting on the crankshaft 12 only in a forward direction, a secondary freewheel 16 arranged coaxially in parallel with the main freewheel 14 and transmitting the torque acting on the crankshaft 12 only in a reverse direction, an idler 18 rotatably disposed around the secondary freewheel 16, a sprocket 20 rotating coaxially with a rear wheel of the bicycle, and a chain 26 hung around each of the main freewheel 14, the idler 18, the secondary freewheel 16, and the sprocket 20 such that, regardless of a rotational direction of the crankshaft 20, the main freewheel 14 always rotates relative to the secondary freewheel 16 in the reverse direction and the sprocket 20 always rotates in the forward direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a bicycle drive mechanism, and more particularly to a bicycle chain drive mechanism that transmits driving force to a rear wheel via a chain. [Background technology]

[0002] Most commonly used bicycle drive mechanisms are a combination of a crank mechanism and a chain and sprocket mechanism. In this type of drive mechanism, the driving force is transmitted to the rear wheel via a chain that rotates as the left and right cranks rotate.

[0003] A typical bicycle is configured so that a freewheel is installed in the rear wheel and torque is transmitted to the wheel axle of the rear wheel only when the left and right cranks rotate forward. Meanwhile, Patent Document 1 discloses a bicycle chain drive mechanism in which driving force is transmitted to the rear wheel not only when the cranks rotate forward but also when they rotate reversely. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Publication No. 56-136877 Summary of the Invention [Problem to be solved by the invention]

[0005] In the bicycle chain drive mechanism disclosed in Patent Document 1, two freewheels are attached to the hub of the rear wheel. Idlers are provided below the freewheels, and a chain is hung on the upper gear portion of each freewheel via the idlers. This ensures that torque acts in the direction that rotates the rear wheel forward, regardless of whether the chain rotates in the forward or reverse direction as the crank rotates.

[0006] With a bicycle chain drive mechanism configured as described above, the bicycle can be moved forward whether the crank is rotated in the forward or reverse direction, which offers various advantages such as making it easier to ride uphill and eliminating the need to worry about the pedal position when starting. However, when changing gears with the above configuration, it is necessary to change the chain to the upper gear portion of each of the two freewheels, which means that the commonly known externally-used gear shifters cannot be used.

[0007] In view of the above-mentioned problems, the present invention aims to provide a bicycle chain drive mechanism that can transmit driving force to the rear wheel regardless of whether the crankshaft is rotating in either the forward or reverse direction, and that makes it possible to select the use of a known external transmission. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, the bicycle chain drive mechanism of the present invention is characterized in that it comprises a main freewheel that rotates coaxially with the crankshaft of the bicycle and transmits torque acting on the crankshaft only in the forward direction, a secondary freewheel that is arranged coaxially in parallel with the main freewheel and transmits torque acting on the crankshaft only in the reverse direction, an idler that is rotatably arranged around the secondary freewheel, a sprocket that rotates coaxially with the rear wheel of the bicycle, and a chain that is hung on each of the main freewheel, the idler, the secondary freewheel and the sprocket so that, regardless of the rotational direction of the crankshaft, the main freewheel always rotates relative to the secondary freewheel in the reverse direction, and the sprocket always rotates in the forward direction.

[0009] The bicycle also has a rear derailleur including a tension pulley and a guide pulley that are rotatably mounted below the sprockets, and the chain is hung on the sprockets via the tension pulley and the guide pulley.

[0010] The sprocket may include a plurality of gears with different numbers of teeth arranged side by side on the same axis, and the chain may be hung on one of the plurality of gears. Effect of the Invention

[0011] With a bicycle chain drive mechanism having the above configuration, the chain is attached so that the main freewheel always rotates in the reverse direction relative to the secondary freewheel and the sprocket always rotates in the forward direction regardless of the direction of rotation of the crankshaft, so that driving force can be transmitted to the rear wheel whether the crankshaft rotates forward or backward. In this case, the chain always rotates in the same direction, and the configuration around the rear wheel itself is the same as that of existing bicycles that are widely used in general, so it is possible to choose to use a known external derailleur. [Brief description of the drawings]

[0012] [Figure 1] 1 is a side view showing a schematic configuration of a chain drive mechanism of a bicycle according to an embodiment. [Diagram 2] 1 is an enlarged side view showing a main portion of a chain drive mechanism of a bicycle according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a bicycle chain drive mechanism (hereinafter simply referred to as a "drive mechanism") according to the present invention will be described with reference to the drawings.

[0014] The drive mechanism 10 according to the embodiment is a modified version of the basic components used in typical bicycle drive units, with some additions and modifications, and with a more ingenious way of attaching the components. Note that Figures 1 and 2 show a schematic enlarged view of the main parts of the drive mechanism 10, and the basic components used in typical bicycle drive units are not shown.

[0015] As shown in Fig. 1, the drive mechanism 10 includes a crankshaft 12. The crankshaft 12 is journalled via bearings (not shown) inside a bottom bracket (not shown) which is fixed to the bottom of a bicycle frame (not shown). Cranks (not shown) are fixed to both left and right ends of the crankshaft 12. Pedals (not shown) are journalled to the tips of the left and right cranks. A main freewheel 14 and a secondary freewheel 16 are provided side by side at the base end of the right crank.

[0016] The main freewheel 14 is attached coaxially with the crankshaft 12. A known ratchet mechanism (not shown) is provided between the main freewheel 14 and the crankshaft 12, and is configured to transmit torque in only one direction. In this example, the main freewheel 14 is configured to transmit torque acting on the crankshaft 12 only when the main freewheel 14 rotates coaxially with the crankshaft 12 in the forward direction (clockwise in FIG. 1).

[0017] The secondary freewheel 16 is arranged coaxially adjacent to the primary freewheel 14. A known ratchet mechanism (not shown) is also provided between the secondary freewheel 16 and the crankshaft 12, and is configured to transmit torque in only one direction. In this example, the secondary freewheel 16 is configured to transmit torque acting on the crankshaft 12 only when the secondary freewheel 16 rotates coaxially with the crankshaft 12 in the reverse direction (counterclockwise in FIG. 1).

[0018] In this way, in this example, the main freewheel 14 is disposed on the axial center side (inner side) of the crankshaft 12, and the secondary freewheel 16 is disposed on the axial end side (outer side) of the crankshaft 12. Note that in this example, the secondary freewheel 16 has a smaller diameter than the main freewheel 14, but the secondary freewheel 16 may have the same diameter as the main freewheel 14.

[0019] An idler 18 is provided below the secondary freewheel 16. The idler 18 is rotatably supported at the bottom of the bicycle frame (not shown). The idler 18 is configured to rotate about an axis that is approximately parallel to the crankshaft 12, but it may be attached with its rotation axis appropriately inclined relative to the crankshaft 12 depending on factors such as the size of the gap between the main freewheel 14 and the secondary freewheel 16.

[0020] A sprocket 20 that rotates coaxially with the rear wheel (not shown) of the bicycle is provided behind the main freewheel 14 and the secondary freewheel 16. A known ratchet mechanism is provided between the wheel axle of the rear wheel and the sprocket 20, similar to the main freewheel 14 and the secondary freewheel 16 described above, and is configured to transmit torque in only one direction. Therefore, torque is transmitted to the wheel axle of the rear wheel only when the sprocket 20 rotates in the forward direction (clockwise in FIG. 1), the same as the direction in which the rear wheel rotates forward.

[0021] Sprocket 20 is a so-called multi-stage sprocket, and includes multiple gears with different numbers of teeth arranged side by side on the same axis, although these gears are not shown in Fig. 1. The multiple gears are arranged such that the gears closer to the rear wheel have larger diameters, and all the gears are configured to rotate concentrically as a unit.

[0022] A rear derailleur (not shown), which constitutes a well-known external transmission, is provided below sprocket 20. By operating a shifter (not shown), the rear derailleur moves a chain 26, which will be described later, between each gear of sprocket 20 for gear changes. The rear derailleur includes a tension pulley 22 and a guide pulley 24. Tension pulley 22 and guide pulley 24 are each rotatably supported by the derailleur body.

[0023] As described above, the drive mechanism 10 has a total of six transmission gears, including two freewheels 14, 16 and an idler 18 on the drive side (front side), and a sprocket 20, a tension pulley 22, and a guide pulley 24 on the driven side (rear side). An endless chain 26 is hung on each of these six transmission gears.

[0024] The chain 26 is looped around each of the six transmission gears in the following manner. The manner in which the chain 26 is looped will be specifically described with reference to Figs.

[0025] The chain 26 is hung from the upper gear portion to the front gear portion of the main freewheel 14, stretched to the front gear portion of the idler 18, and folded back to the rear gear portion of the idler 18. The folded back chain 26 is hung from the front gear portion to the upper gear portion of the secondary freewheel 16, and folded back to the lower gear portion of the tension pulley 22. Furthermore, the chain 26 folded back to the upper gear portion of the tension pulley 22 passes through the front gear portion of the guide pulley 24, is hung from the rear gear portion to the upper gear portion of the sprocket 20 (one of the multiple gears), and is then folded back to the upper gear portion of the main freewheel 14.

[0026] With this arrangement, the chain 26 looped around each of the six transmission gears always repeats circular movement in the same direction so that the main freewheel 14 always rotates in the reverse direction relative to the sub freewheel 16 and the sprocket 20 always rotates in the forward direction, regardless of the rotational direction of the crankshaft 12. The operation of this driving device 10 will now be described in detail with reference to the drawings.

[0027] First, the movement of the crankshaft 12 when it rotates in the normal direction will be described.

[0028] When the crankshaft 12 rotates in the forward direction, the main freewheel 14 also rotates coaxially with the crankshaft 12. At this time, the torque acting on the crankshaft 12 is transmitted, so the chain 26, which is located behind the upper gear portion of the main freewheel 14, is pulled forward and moves from the front gear portion of the main freewheel 14 toward the idler 18. As the chain 26 moves, the idler 18 guides the chain 26 to the front gear portion of the secondary freewheel 16 while rotating in the forward direction (clockwise).

[0029] As the chain 26 moves as described above, the secondary freewheel 16 rotates in the reverse direction opposite to the rotational direction of the crankshaft 12, but the torque acting on the crankshaft 12 is not transmitted to the rotation of the secondary freewheel 16. Therefore, in this case, the secondary freewheel 16 functions as a second idler that guides the chain 26 to the tension pulley 22.

[0030] The movement of the chain 26 guided to the sprocket 20 via the tension pulley 22 and guide pulley 24 causes the sprocket 20 to rotate in the normal direction, thereby transmitting torque to the wheel axle of the rear wheel. The chain 26 then moves again to the main freewheel 14 side via the sprocket 20. Through this series of events, the chain 26 repeats circular movement on an endless track.

[0031] Next, the movement of the crankshaft 12 when it rotates in the reverse direction will be described.

[0032] When the crankshaft 12 rotates in the reverse direction, the torque acting on the crankshaft 12 is not transmitted to the main freewheel 14, and the secondary freewheel 16 rotates coaxially with the crankshaft 12. At this time, the torque acting on the crankshaft 12 is transmitted, so that the chain 26 hung on the secondary freewheel 16 is pulled and moves toward the tension pulley 22. Then, the movement of the chain 26 guided to the sprocket 20 via the tension pulley 22 and guide pulley 24 causes the sprocket 20 to rotate in the forward direction, and as a result, the torque is transmitted to the wheel axle of the rear wheel.

[0033] The chain 26 then moves from the sprocket 20 to the idler 18 via the upper gear portion and the front gear portion of the main freewheel 14. As the chain 26 moves, the main freewheel 14 rotates in the normal direction opposite to the rotational direction of the crankshaft 12, but the torque acting on the crankshaft 12 is not transmitted to the rotation of the main freewheel 14. Therefore, in this case, the main freewheel 14 functions as a third idler that guides the chain 26 to the idler 18.

[0034] The chain 26, which has been guided to the idler 18, moves again toward the secondary freewheel 16. Through this series of steps, the chain 26 repeats circular movement on an endless track.

[0035] Thus, according to the drive mechanism 10 of the embodiment, the chain 26 is looped so that the main freewheel 14 always rotates in the reverse direction relative to the secondary freewheel 12 and the sprocket 20 always rotates in the forward direction, regardless of the rotation direction of the crankshaft 12, so that driving force can be transmitted to the rear wheel whether the crankshaft 12 rotates forward or backward. At this time, the chain 26 always moves in the same direction (the direction shown by the arrow in Figure 1), so the configuration around the rear wheel itself is the same as that of existing bicycles that are widely used by the general public, and it is possible to select the use of a known external transmission.

[0036] The above describes the bicycle chain drive mechanism of the present invention based on an embodiment, but the present invention is of course not limited to the above-mentioned embodiment, and may be embodied in modified forms, for example, as follows.

[0037] <Variation 1> The manner in which the chain is routed described in the above embodiment is merely an example, and other arrangements may be used. For example, the arrangement and number of idlers may be changed as long as they are provided around the secondary freewheel.

[0038] The present invention can be implemented in various forms that include improvements, modifications, or variations based on the knowledge of a person skilled in the art without departing from the spirit of the present invention. In addition, the present invention can be implemented in a form in which any of the invention-specific features are replaced with other technologies within the scope of the same action or effect. [Explanation of symbols]

[0039] 10 Bicycle chain drive mechanism 12 Crankshaft 14 Main freewheel 16 Secondary freewheel 18 Idler 20 Sprockets 22 Tension pulley 24 Guide pulley 26 Chain

Claims

1. A main freewheel that rotates coaxially with a crankshaft of a bicycle and transmits torque acting on the crankshaft only in the forward direction; a secondary freewheel arranged coaxially with the primary freewheel and configured to transmit torque acting on the crankshaft only in a reverse direction; an idler rotatably mounted around the secondary freewheel; a sprocket that rotates coaxially with the rear wheel of the bicycle; a chain that is wound around each of the main freewheel, the idler, the secondary freewheel, and the sprocket so that the main freewheel always rotates in a reverse direction relative to the secondary freewheel and the sprocket always rotates in a normal direction regardless of a rotational direction of the crankshaft; A bicycle chain drive mechanism comprising:

2. a rear derailleur including a tension pulley and a guide pulley each rotatably disposed below the sprocket, 2. The bicycle chain drive mechanism according to claim 1, wherein the chain is looped around the sprocket via the tension pulley and the guide pulley.

3. The sprocket includes a plurality of gears having different numbers of teeth arranged side by side on the same axis, 3. The bicycle chain drive mechanism according to claim 2, wherein the chain is looped around one of the plurality of gears.

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