A transmission device assembly for a bicycle

Abstract: A transmission device for a bicycle, the transmission device comprising : a first transmission means for obtaining forward driving force by driving a first free wheel (10) in conformity to a movement of a first drive unit when a crank shaft (9) is forwardly rotated ; and, a second transmission means for obtaining forward driving force by converting a direction of the rotating force produced in a rotational direction of a second drive unit, the rotational direction being supplied to a second free wheel (22) under a reverse rotation of the crank shaft (9), whereby obtaining forward driving force regardless a rotational direction of the crank shaft (9) to improve an effect of exercise.

Description: The present invention relates to a transmission device for a bicycle, which allows to continously obtain the forward driving force even if the crank shaft is changed in rotational direction forwardly or reversely. From GB-A-2 143 599 there is known a transmission device for a bicycle according to the preamble of claims 1 and 3. This known device uses one chain to drive two adjacent gear-wheels in two different directions respectively when the pedals are rotated in one direction; free-wheeling devices select the engagement of a transmission ratio in dependance of pedal rotation. With another conventional bicycle (see Fig.1), forward driving force can only be obtained if a crank shaft is rotated in a forward direction. The bicycle generally includes a forward fork 2 for mounting a front wheel 1 ; a backward fork 4 for mounting a rear wheel 3 ; and a frame F having a cross bar 5 for connecting the forks 3 and 4 with each other. The frame F has diagonally extended forward and backward bars 6 and 7 of which lower end portion is integrally connected to a general hub. Moreover, a chain gear 8 and a pair of pedals are coupled operationally to a crank shaft 9, and a driven gear wheel 10 including free-wheeling means is coupled to a backward hub. Also, a driving chain 11 is engaged with the peripheral portions of the chain gear 8 and the driven gear wheel 10 so as to obtain a driving force of the bicycle according to the rotation thereof. With the transmission device for the bicycle constructed as described above, the driving chain 11 is disposed so that, when the crank shaft 9 is rotated, the driven gear wheel 10 including free-wheeling means is rotated in a direction equal to the rotational direction of the crank shaft 9. As a result, when the crank shaft 9 is rotated in a forward direction, the forward driving force can be produced. Alternatively, if the crank shaft 9 is rotated in a reverse direction, the forward driving force can't be produced since the driven gear wheel 10 is in an idle or free-wheeling state. Accordingly, for obtaining the forward driving force for the bicycle, the latter must be handled in a constant driving direction. Therefore, there are defects that the driving operation is monotonized and an effect of exercise is unsufficient. The device known from GB-A-2 143 599 suffers from the fact that the chain is bent out at its ideal working plane for looping around the second gear wheel, which results in the necessity of a relatively long chain. Accordingly, the present invention has been made to solve the afore-mentioned defects and an object of the invention is to provide an alternative simple transmission device for a bicycle, wherein forward driving force can be produced even if a crank shaft of the bicycle is rotated forwardly or backwardly. Another object of the invention is to provide a transmission device for a bicycle, wherein a forward motion velocity obtained in case that a crank shaft is reversely rotated can be changed. According to one aspect of the invention there is provided a transmission device for a bicycle as set out in claim 1. According to another aspect of the invention there is provided a transmission device for a bicycle as set out in claim 3. Preferred embodiments of the invention are subjects of claims 2 and 4 to 7. The above and other objects, features and advantages will become apparent from the following description taken with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a bicycle according to a conventional construction ; Fig. 2 is a perspective view of a bicycle having a transmission device according to the present invention ; Figs. 3 to 6 are views illustrating different examples of the transmission device for a bicycle according to the present invention ; Fig. 7 is a view showing a driving chain guide mechanism which is used for the transmission device for the bicycle in Fig. 6 ; and, Figs. 8 and 9 are views showing modified examples of the guide mechanism used for the transmission device for a bicycle according to the present invention. Thereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. Referring to Fig. 2, there is shown a perspective view of a bicycle in which a transmission device according to the present invention is additionally employed to conventional bicycle transmission means. In the drawing, a first transmission means includes a first chain gear 8, a first gear wheel 10 including free-wheeling means and a first driving chain 11, which are fixedly assembled to a side portion of a crank shaft and a hub of a rear wheel 3. A second transmission means includes a second driving chain 21 rotated by a second chain gear 20 fixedly coupled to the crank shaft 9, a tension pulley 23 and a guide pulley 24 which are coupled to the hub of the rear wheel 3, and is fixed to the hub of the rear wheel 3 so that a second gear wheel 22 including free-wheeling means is positioned between the tension pulley 23 and the guide pulley 24, as shown in Fig.3. Moreover, sprockets (not shown)of the gear wheels 10 and 22 of the bicycle shown in Fig.2 are rotated in an opposite direction with each other. According to the transmission device for the bicycle of the present invention, if the crank shaft 9 is forwardly rotated, the forward driving force is obtained by the first transmission means having a conventional construction. Also, if the crank shaft is reversely rotated, the forward driving force is obtained by the second transmission means according to the present invention. Now, an operation in which the forward driving force is always obtained even if the rotational direction of the crank shaft is changed by means of the transmission device for the bicycle thus constructed will be effected as follows. In Fig. 2, when the crank shaft 9 is rotated in a clockwise direction, that is, in a forward direction, the first and second chain gears 8 and 20 are forwardly rotated while the first and second gear wheels 10 and 22 are rotated in the opposite direction with each other by means of the first and second driving chains 11 and 21. In this case, the rotational force of the sprocket of the first gear wheel 10 is transferred to the first gear wheel 10 to thereby obtain the forward driving force. At this time, the sprocket of the second gear wheel 22 is rotated in a direction opposite to that of the first gear wheel 10 by the tension pulley 23 shown in Fig. 3, in other words, the second gear wheel 22 is idling or in a free-wheeling state. On the contrary, when the crank shaft 9 is rotated in a counterclockwise direction, that is, in a reverse direction, the first and second chain gears 8 and 20 are rotated and the first and second driving chains 11 and 21 are also rotated, so that the sprocket of the first gear wheel 10 is idling or in a free-wheeling state while the sprocket of the second gear wheel 22 is forwardly rotated to obtain the forward driving force. Figs. 4 and 5 show views illustrating modified examples of the second transmission means according to the present invention. In the second transmission means shown in Fig. 4, the second driving chain 21 is disposed to rotate about the second chain gear 20 and the tension pulley 23. This tension pulley 23 is fixed to a gear 23A having a given size by means of a fixing pin, and the second gear wheel 22 is engaged with the gear 23A. According to the second transmission means thus constructed, it is possible to obtain the forward driving force as the crank shaft 9 is reversely rotated. More particularly, if the crank shaft 9 is reversely rotated, then the tension pulley 23 and the gear 23A coupled to the tension pulley 23 are reversely rotated and the second gear wheel 22 is forwardly rotated, so that the forward driving force is produced for driving the bicycle. Meanwhile, the second transmission means shown in Fig. 5 has the second driving chain 21 which is passed around the second gear wheel 22 inform of a 4 00" shape. With the second transmission means, the second gear wheel 22 is rotated in a direction opposite to that of the second chain gear 20 to thereby obtain the forward driving force. Referring to Fig. 6, there is shown a preferred embodiment of the second transmission means according to the present invention. With the transmission means in Fig. 6, a chain guide mechanism A is disposed at an upward side of the second gear wheel 22 including free-wheeling means mounted on the hub so that rotational force of the second driving chain 21 rotated by the second chain gear 20 is provided to the guide mechanism A and the second gear wheel 22, and the second gear wheel 22 is disposed so as to contact an outer lower side of the preriphery of the driving chain 21. In the second transmission means arranged as described above, if the crank shaft 9 is reversely rotated, the second gear wheel 22 is forwardly rotated while the tension pulley 23 and the guide pulley 24 of the guide mechanism are reversely rotated, so that the bicycle having the afore-mentioned second transmission means enables to take the forward driving force even if the crank shaft 9 is reversely rotated. Moreover, in the guide mechanism a stationary member 26 is fixed to a shaft of the hub, a chain guide 25 having the tension pulley 23 and the guide pulley 24 coupled thereto is supported toward the stationary member 26 by means of a horizontal pin 27, and a tension spring 28 is disposed between the chain guide 25 and the stationary member 26 to rotate the chain guide 25 in a counterclockwise direction relative and around the horizontal pin 27 so as to provide a certain tension to the driving chain. Referring to Figs. 8 and 9, there are shown different guide machanisms for changing the forwardly running velocity, which are employed to the second transmission means according to the present invention, respectively. In the drawings, a fixed member 30 is fixedly connected to a shaft of the hub and a supporting member 31 is movably supported toward the fixed member 30 by means of a first horizontal pin 32A. The supporting member 31 has a pair of link members 33 and 34 oppositely spaced at a certain distance, a support element 35 for supporting a casing (not shown) for guiding a control wire and a fixing element 36 for fixing the support element 35. The link members 33 and 34 are located at respective one ends between supporting arms 31a and 31b of the supporting member 31 and movably supported toward the supporting member 31 by first and second vertical pins 37a and 37b. Also, a movable member 38 is movably connected to the other ends of the link members 33 and 34 by means of third and fourth vertical pins 37c and 37d. The movable member 38 has a shape similar to that of the supporting member 31 and includes connecting arms 38a and 38b for connecting it with the link members 33 and 34 and a fixing element 36 for fixing one end of the control wire. The movable member 38 movably supports the chain guide 25 having two pulleys, around and relative to the horizontal pin 27 so as to provide a certain tension to the driving chain. As shown in Fig. 9 and, due to the movement of the movable member 38, the driving chain 21 engaged with one sprocket of the second gear wheel 22 can be engaged with the other sprocket.

Claims: A transmission device for a bicycle, which comprising: a first transmission means (8, 10, 11) for obtaining a forward driving force by driving a first gear wheel (11) including free-wheeling and coupled to a hub of a rear wheel (3) in conformity to a movement of a first drive unit when a crank shaft (9) is forwardly rotated; and, a second transmission means (20, 21, 22, 23, 24) for obtaining the forward driving force by a rotating force produced in a rotational direction of a second drive unit, the rotational direction being provided to a second gear wheel (22) including free wheeling under a reverse rotation of said crank shaft (9), characterized in that said second transmission means includes a second driving chain (21) rotated by a second chain gear (20) fixedly coupled to said crank shaft (9), a tension pulley (23) and a guide pulley (24) which are coupled to said hub of said rear wheel (3). A transmission device for a bicycle according to claim 1, wherein said second gear wheel (22) is positioned between said tension pulley (23) and said guide pulley (24). A transmission device for a bicycle according to the preamble of claim 1, wherein said second transmission means comprises a second driving chain (21) rotated along the periphery of a second chain gear (20) and a tension pulley (23), a gear (23A) having a given size fixed to said tension pulley (23) by means of a fixing pin, and said second gear wheel (22) is engaged with said gear (23A). A transmission device for a bicycle according to claim 1, wherein said second transmission means includes a chain guide mechanism positioned at an upward side of said second gear wheel (22) including free-wheeling and mounted on said rear wheel (3) so that rotational force of said second driving chain (21) rotated by means of said second chain gear (20) is sequentially provided to said guide mechanism and said second gear wheel (22), and said second gear wheel (22) is disposed so that to contact an outer lower side of the periphery of said driving chain (21). A transmission device for a bicycle according to claim 1, further comprising a chain guide mechanism including: a fixing member (26) having an end fixedly connected to said hub and a supporting frame; a horizontal pin (27) for connecting a chain guide (25) having said tension pulley (23) and guide pulley (24) to said fixing member (26); and a tension spring (28) disposed between said fixing member (26) and said chain guide (25). A transmission device for a bicycle according to claim 4, wherein said tension spring (28) is arranged to rotate said chain guide (25) in a direction relative and around said horizontal pin (27) to provide a certain tension to the driving chain (21). A transmission device for a bicycle according to claim 3, wherein said guide mechanism is arranged so that two link members (33, 34) are coupled between a supporting member (31) and a movable member (38) fixed by a horizontal pin (32A) and tension springs (39, 40) are disposed between said supporting member (31) and a fixed member (30) and also between said movable member (38) and a chain guide (25) by one and one to thereby move along a curved trajectory said movable member (38) and said chain guide (25) in a direction relative and around first and second vertical pins (37c, 37d) to provide a certain tension to the driving chain (21).

Inventors: CHUNG-SUK KIM, CHUNG-SUK, KIM
Applicants: CHUNG SUK KIM, CHUNG-SUK, KIM
Application year: 1992
Main classification: B62M1
IPC codes: B62M11, B62M1, B62M9