Bicycle chain drive mechanism

Abstract

[PROBLEM] To make it possible to choose to use a known external transmission, in a bicycle chain drive mechanism that can transmit a drive force to a rear wheel, regardless of the rotational direction of a crank shaft being forward or reverse. [SOLUTION] The present invention is provided with: a main free wheel 14 that rotates coaxially with a crank shaft 12 of a bicycle and that transmits, only in the forward rotational direction, a torque acting on a crank shaft 12; a sub-free-wheel 16 that is juxtaposed coaxially with the main free wheel 14 and transmits, only in a reverse rotational direction, a torque acting on the crank shaft 12; an idler 18 rotatably provided around the sub-free-wheel 16; a sprocket 20 that rotates coaxially with the rear wheel of the bicycle; and a chain 26 engaged with each of the main free wheel 14, the idler 18, the sub-free-wheel 16 and the sprocket 20 such that, regardless of the rotational direction of the crank shaft 20, the main free wheel 14 always rotates relatively in the opposite direction of the sub-free-wheel 16 and the sprocket 20 always rotates in the forward rotation direction.

Description

Bicycle chain drive mechanism

[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.

[0002] Most commonly used bicycle drivetrains are comprised of a crank mechanism and a chain and sprocket mechanism. In this type of drivetrain, 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 has a freewheel built into the rear wheel, and is configured so that torque is transmitted to the rear wheel axle only when the left and right cranks rotate forward. On the other hand, Patent Document 1 discloses a bicycle chain drive mechanism that transmits driving force to the rear wheel not only when the cranks rotate forward, but also when they rotate reversely.

[0004] Jitszen No. 56-136877

[0005] The bicycle chain drive mechanism disclosed in Patent Document 1 has two freewheels mounted on the hub of the rear wheel. Idlers are mounted below the freewheels, and a chain is looped around the upper gear of each freewheel via these idlers. This ensures that torque acts in the direction that rotates the rear wheel forward, regardless of whether the chain rotates forward or backward as the crank rotates.

[0006] A bicycle chain drive mechanism with the above configuration allows the bicycle to move forward whether the crank is turned forward or backward, 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 of each of the two freewheels, which means that widely used, well-known external derailleurs 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 allows the use of a known external derailleur.

[0008] In order to achieve the above object, the bicycle chain drive mechanism of the present invention is characterized by comprising: 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 with the main freewheel and transmits torque acting on the crankshaft only in the reverse direction; an idler that is rotatably mounted around the secondary freewheel; a sprocket that rotates coaxially with the rear wheel of the bicycle; and 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 the reverse direction relative to the secondary freewheel and the sprocket always rotates in the forward direction, regardless of the rotational direction of the crankshaft.

[0009] Furthermore, the present invention is characterized in that it is provided with a rear derailleur including a tension pulley and a guide pulley that are rotatably mounted below the sprocket, and the chain is hung on the sprocket 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 looped around one of the plurality of gears.

[0011] With a bicycle chain drive mechanism configured as described above, the chain is fastened so that the primary 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. This means that driving force can be transmitted to the rear wheel regardless of whether the crankshaft rotates forward or backward. Since the chain always rotates in the same direction, and the configuration around the rear wheel itself is the same as that of widely used existing bicycles, it is possible to use a known external derailleur.

[0012] 1 is a side view showing a schematic configuration of a bicycle chain drive mechanism according to an embodiment, and FIG. 2 is an enlarged side view showing a main part of the bicycle chain drive mechanism according to an embodiment.

[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 a typical bicycle drive unit, with some additions and modifications made to the way those components are attached. Figures 1 and 2 show a schematic, enlarged view of the main parts of the drive mechanism 10, and do not show the basic components used in a typical bicycle drive unit.

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

[0016] The main freewheel 14 is mounted 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 coaxially arranged 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 torque acting on the crankshaft 12 is transmitted 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 (inside) of the crankshaft 12, and the secondary freewheel 16 is disposed on the axial end side (outside) 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 around an axis that is approximately parallel to the crankshaft 12, but it may also be mounted with its rotation axis appropriately inclined relative to the crankshaft 12, depending on factors such as the size of the gap between the primary freewheel 14 and 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 secondary freewheel 16. A known ratchet mechanism, similar to that of the main freewheel 14 and secondary freewheel 16, is provided between the rear wheel axle and sprocket 20, and is configured to transmit torque in only one direction. Therefore, torque is transmitted to the rear wheel axle only when the sprocket 20 rotates in the forward direction (clockwise in FIG. 1), the same direction in which the rear wheel rotates forward.

[0021] The 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 Figure 1. The gears are arranged so that the diameters of the gears increase as they approach the rear wheel, and all of 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 the sprocket 20. The rear derailleur moves a chain 26 (described below) between each gear of the sprocket 20 to change gears when a shifter (not shown) is operated. The rear derailleur includes a tension pulley 22 and a guide pulley 24. The tension pulley 22 and the 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: 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 looped around 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 hooked from the upper gear portion to the front gear portion of the main freewheel 14, passed over to the front gear portion of the idler 18, and then folded back to the rear gear portion of the idler 18. The folded back chain 26 is hooked from the front gear portion to the upper gear portion of the secondary freewheel 16, and passed over to the lower gear portion of the tension pulley 22. Furthermore, the chain 26 that has been folded back to the upper gear portion of the tension pulley 22 passes through the front gear portion of the guide pulley 24, is hooked from the rear gear portion to the upper gear portion of the sprocket 20 (one of the multiple gears), and passed over 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 primary freewheel 14 always rotates in the reverse direction relative to the secondary 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 drive unit 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, 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 rotates in the forward direction (clockwise) and guides the chain 26 to the front gear portion of the secondary freewheel 16.

[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, which is guided to the sprocket 20 via the tension pulley 22 and guide pulley 24, causes the sprocket 20 to rotate in the forward direction, thereby transmitting torque to the rear wheel axle. The chain 26 then moves again toward the main freewheel 14 via the sprocket 20. Through this series of events, the chain 26 repeatedly moves in an endless orbit.

[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 the chain 26 attached to 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, 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 front gear portion of the main freewheel 14. As the chain 26 moves, the main freewheel 14 rotates in the forward 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] As described above, with the drive mechanism 10 according to this embodiment, the chain 26 is looped so that the primary 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 rotational direction of the crankshaft 12. This allows for the transmission of driving force to the rear wheel regardless of the rotational direction of the crankshaft 12. In this case, the chain 26 always moves in the same direction (the direction indicated by the arrow in Figure 1), so the configuration around the rear wheel itself can be the same as that of existing bicycles that are widely used, and it is possible to choose to use a known external transmission.

[0036] The above describes the bicycle chain drive mechanism of the present invention based on an embodiment, but it goes without saying that the present invention is not limited to the above-mentioned form, and it may be embodied in modified forms, for example, as follows.

[0037] <Modification 1> The chain routing described in the above embodiment is merely an example, and other configurations are possible. For example, the arrangement and number of idlers can be modified as long as they are provided around the secondary freewheel.

[0038] The present invention can be implemented in various forms, including improvements, modifications, and variations based on the knowledge of those skilled in the art, without departing from the spirit of the invention. Furthermore, the invention can be implemented in a form in which any of the features of the invention are replaced with other technology, as long as the same action or effect is achieved.

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

Claims

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

2. A bicycle chain drive mechanism as described in claim 1, further comprising a rear derailleur including a tension pulley and a guide pulley each rotatably mounted below the sprocket, and the chain is hung on the sprocket via the tension pulley and the guide pulley.

3. A bicycle chain drive mechanism as described in claim 2, wherein the sprocket includes a plurality of gears with different numbers of teeth arranged side by side on the same axis, and the chain is hung on one of the plurality of gears.

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