A three-stage bicycle transmission and a bicycle

Abstract

The present invention discloses a three-stage bicycle transmission and a bicycle, relating to the technical field of bicycles, including a speed regulator disposed on the handlebar and a speed-changing piece on the vehicle body. The speed regulator and the speed-changing piece are connected by a speed-changing wire. It includes a three-stage transmission, and the three-stage transmission includes a gear-changing disc, a low-speed chain wheel, a medium-speed chain wheel, a high-speed chain wheel and a crank which are sequentially combined in order. The low-speed chain wheel is fixedly connected to the crank, and the medium-speed chain wheel and the high-speed chain wheel are connected to the crank through bearings. The low-speed chain wheel, the medium-speed chain wheel and the high-speed chain wheel are respectively and independently connected with a chain. A linkage mechanism is provided on the crank, and a gear-changing mechanism is provided on the gear-changing disc. In the present invention, the low-speed chain wheel, the medium-speed chain wheel and the high-speed chain wheel respectively drive their own chains, and the gear-changing disc controls the gear shifting. The gear shifting is smooth and easy, with a 360-degree dead-free angle, and the chain will not be shifted to cause chain derailment. Moreover, all internal parts are realized through mechanical structures and do not involve any electronic devices, so the production and manufacturing cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of bicycles, and particularly relates to a three-stage bicycle transmission and a bicycle. Background Art

[0002] A bicycle shifter is used for shifting gears of a bicycle transmission. The shifter is connected to the bicycle transmission through a control cable for shifting operations. Currently, during the shifting process, by switching the bicycle chain to cooperate with different-sized sprocket discs, when adjusting the speed, the derailleur is pulled by the cable to shift the chain from the current flywheel to the next flywheel to complete the gear shift, thereby adjusting the transmission ratio of the front and rear gears and the driving pedaling force to meet different usage requirements. However, this shifting method has the following problems: 1. The chain is prone to derailment during the gear shift, causing inconvenience to the user. 2. The shifting is strenuous and continuous force needs to be applied by hand to completely shift the chain to the next flywheel. Summary of the Invention

[0003] The purpose of the present invention is to provide a three-stage bicycle transmission and a bicycle to solve the problems raised in the above background art.

[0004] To achieve the above purpose, the present invention provides the following technical solution: A three-stage bicycle transmission includes a shifter provided on the handlebar and a shift piece on the vehicle body. The shifter and the shift piece are connected by a shift cable. It includes a three-stage transmission, and the three-stage transmission includes a shift disc, a low-speed chain disc, a medium-speed chain disc, a high-speed chain disc, and a crank that are sequentially combined. The low-speed chain disc is fixedly connected to the crank. The medium-speed chain disc and the high-speed chain disc are connected to the crank through bearings. The low-speed chain disc, the medium-speed chain disc, and the high-speed chain disc are each separately connected to a chain. A linkage mechanism is provided on the crank, and a shifting mechanism is provided on the shift disc. The medium-speed chain disc and the high-speed chain disc are controlled by the interaction between the shifting mechanism on the shift disc and the linkage mechanism on the crank. The shift disc is in contact connection with the shift piece.

[0005] Further preferably, the linkage mechanism includes a crank arm, a rotating shaft, a medium-speed chain disc control key, and a high-speed chain disc control key. The crank arm and the rotating shaft are fixedly connected. The high-speed chain disc control key is connected to the end of the crank arm through a limiting component. A chute is provided on the side wall of the rotating shaft, and the medium-speed chain disc control key is connected to the chute on the side wall of the rotating shaft through a second spring.

[0006] Preferably, the limit assembly comprises a fixing frame and a fixing cover plate, the middle portion of the fixing frame is a square through hole, the end of the fixing frame is provided with a screw hole, the side end of the fixing cover plate is provided with a corresponding through hole, and a circular through hole is provided at a position on the end face of the rotating shaft corresponding to the square through hole in the middle portion of the fixing frame, the high-speed chain disk control key is a square block, one end of which is provided with a protrusion, and the other end of the same side is provided with a circular column, the end face of the protrusion is an inclined surface, the end of the high-speed chain disk control key opposite to the circular column is provided with a circular hole, and a third spring is provided in the circular hole, the medium-speed chain disk control key is an L-shaped plate, one end of which is provided with a circular hole, and a second spring is provided in the circular hole, and the end face of the other side of the L-shape is provided with a groove, the high-speed chain disk control key is movably connected to the square through hole in the middle portion of the fixing frame through the third spring, and the circular column at its end passes through the circular through hole on the rotating shaft.

[0007] Preferably, the gear shifting mechanism comprises a first rotating disk and a second rotating disk, and the second rotating disk is rotatably connected to the first rotating disk;

[0008] The first turntable is provided with a medium-speed guide groove and a high-speed guide groove, and a V-shaped limit block is provided in the medium-speed guide groove and the high-speed guide groove. The V-shaped limit block is connected in the groove by a pin, and the V-shaped limit block can rotate in the groove. A return spring is connected to the bottom of the pin to limit the rotation of the V-shaped limit block. At least one side of the medium-speed guide groove and the high-speed guide groove is connected to a return tension spring, and the other end of the return tension spring is connected to the second turntable. The first turntable is provided with a medium-speed small bearing and a high-speed small bearing;

[0009] The second turntable is provided with a medium-speed turn rod and a high-speed turn rod, one end of the medium-speed turn rod and the high-speed turn rod are rotatably connected to the second turntable, and the other end is provided with a support rod, which extends into the medium-speed guide groove and the high-speed guide groove and can slide in the groove. The middle part of the medium-speed turn rod and the high-speed turn rod is connected with a limiting spring so that they always lean towards the center of the second turntable. The middle part of the second turntable is provided with a first give way groove and a second give way groove, and an adjustment component is provided at the first give way groove.

[0010] Preferably, the adjustment assembly includes an adjustment rod, a connecting plate, and a pull plate, the middle portion of the adjustment rod is rotatably connected to the connecting plate, the end portion of the adjustment rod is fixedly connected to the pull plate, the connecting plate is fixed on the second turntable, and the pull plate is connected to the second turntable via a spring.

[0011] Preferably, the low-speed chain disc is connected with a medium-speed pressure-changing component and a high-speed pressure-changing component via a movable shaft, and the medium-speed pressure-changing component is provided with a pressure rod, which can be pressed into the groove of the medium-speed chain disc control key as the medium-speed pressure-changing component rotates, and the high-speed pressure-changing component is in contact with the adjustment rod of the adjustment assembly.

[0012] Preferably, a coaxial circular ring shaft is provided in the middle of the medium-speed chain wheel and the high-speed chain wheel, and helical teeth are provided on the end face of the circular ring shaft.

[0013] Preferably, the medium-speed chain wheel control key and the high-speed chain wheel control key have the same width.

[0014] Preferably, washers are respectively provided between the shift disc, the low-speed chain wheel, the medium-speed chain wheel, and the high-speed chain wheel.

[0015] Another object of the present invention is to provide a bicycle including the above-mentioned three-speed bicycle transmission.

[0016] In the above technical solution, the technical effects and advantages provided by the present invention are as follows:

[0017] 1. In the present invention, the low-speed chain wheel, the medium-speed chain wheel, and the high-speed chain wheel respectively drive their respective chains, and the shift disc controls the gear shift. The gear shift is smooth and easy, with a 360-degree dead angle-free, and the chain will not be disengaged. Moreover, the internal parts are all realized through mechanical structures and do not involve any electronic devices, so the production and manufacturing cost is low.

[0018] 2. Through the ingenious structural design, the present invention can respectively control different chain wheels to achieve different speed ratio effects, with fast, flexible, and few-fault shifting, no time difference, and long service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings.

[0020] Figure 1 It is a schematic structural diagram of the shift disc of the present invention;

[0021] Figure 2 It is a schematic structural diagram of the first turntable of the present invention;

[0022] Figure 3 It is a schematic structural diagram of the second turntable of the present invention;

[0023] Figure 4 It is a schematic structural diagram of the adjustment assembly of the present invention;

[0024] Figure 5 It is a schematic structural diagram of the crank linkage mechanism of the present invention;

[0025] Figure 6 It is an exploded schematic diagram of the crank linkage mechanism of the present invention;

[0026] Figure 7Schematic diagram of the low-speed chain wheel structure of the present invention;

[0027] Figure 8 Schematic diagram of the medium-speed chain wheel structure of the present invention;

[0028] Figure 9 Schematic diagram of the high-speed chain wheel structure of the present invention;

[0029] Figure 10 Schematic diagram of the circular ring shaft structure of the medium-speed chain wheel and high-speed chain wheel of the present invention.

[0030] Description of reference numerals:

[0031] 1 - Shift disc; 2 - Limit component; 3 - Protrusion; 4 - Circular column; 5 - Groove; 6 - Second spring; 7 - Third spring; 8 - First turntable; 9 - Second turntable; 12 - Low-speed chain wheel; 13 - Medium-speed chain wheel; 14 - High-speed chain wheel; 15 - And crank; 16 - Circular ring shaft; 1501 - Crank arm; 1502 - Rotating shaft; 1503 - Medium-speed chain wheel control key; 1504 - High-speed chain wheel control key; 201 - Fixed frame; 202 - Fixed cover plate; 801 - Medium-speed guide groove; 802 - V-shaped limit block; 803 - Pin; 804 - Return tension spring; 805 - Medium-speed small bearing; 806 - High-speed small bearing; 807 - High-speed guide groove; 901 - Medium-speed rotating rod; 902 - Support rod; 903 - Limit spring; 904 - First relief groove; 905 - Second relief groove; 906 - High-speed rotating rod 100 - Adjustment component; 1001 - Adjustment rod; 1002 - Connecting plate; 1003 - Pulling plate; 1201 - Medium-speed pressure change part; 1202 - Pressure rod; 1203 - High-speed pressure change part. Detailed implementation manners

[0032] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0033] As Figures 1-10 shown, a three-stage bicycle transmission includes a speed regulator provided on the handlebar and a speed change piece on the vehicle body. The speed regulator is connected to the speed change piece through a speed change wire. It includes a three-stage transmission. The three-stage transmission includes a shift disc 1, a low-speed chain wheel 12, a medium-speed chain wheel 13, a high-speed chain wheel 14, and a crank 15 that are sequentially combined in order. The low-speed chain wheel 12 is fixedly connected to the crank 15. The medium-speed chain wheel 13 and the high-speed chain wheel 14 are connected to the crank 15 through bearings. The low-speed chain wheel 12, the medium-speed chain wheel 13, and the high-speed chain wheel 14 are respectively connected with a chain alone. A linkage mechanism is provided on the crank 15, and a shifting mechanism is provided on the shift disc 1. The medium-speed chain wheel 13 and the high-speed chain wheel 14 are controlled by the interaction between the shifting mechanism on the shift disc 1 and the linkage mechanism on the crank 15. The shift disc 1 is in contact connection with the speed change piece.

[0034] Twist the speed regulator on the handlebar to generate friction between the shift plate and the shift disc 1, limit the rotation of the outer ring of the shift disc 1, the shift mechanism takes effect, the control key of the internal parts of the shift disc 1 is displaced, and the medium-speed chain disc 13 is controlled, and the vehicle moves forward at a medium speed; when a high speed is required, twist the speed regulator again, the shift plate and the shift disc 1 generate friction again, the shift disc 1 controls the high-speed chain disc 14, and the vehicle moves forward at a high speed; when a low gear is required, twist the speed regulator again, and the vehicle returns to the low-speed gear position. Each chain disc is separately connected to its own chain, and there is no situation of shifting gears by shifting the chain. The circular shift disc 1 shifts 360 degrees without dead angles, and the speed is fast and flexible, with few failures, no time difference, and a long service life. When the shift plate and the shift disc 1 are not working, the distance between them is 10mm, which will not affect normal operation.

[0035] Further preferably, Figure 5 , 6 As shown, the linkage mechanism includes a crank arm 1501, a rotating shaft 1502, a medium-speed chain disc control key 1503, and a high-speed chain disc control key 1504. The crank arm 1501 and the rotating shaft 1502 are fixedly connected. The high-speed chain disc control key 1504 is connected to the end of the crank arm 1501 through a limiting assembly 2. A sliding groove is provided on the side wall of the rotating shaft 1502. The medium-speed chain disc control key 1503 is connected to the sliding groove on the side wall of the rotating shaft 1502 through a second spring 6.

[0036] Preferably, the limit assembly 2 includes a fixed frame 201 and a fixed cover plate 202. The fixed frame 201 has a square through hole in the middle, a screw hole is provided at the end of the fixed frame 201, and a corresponding through hole is provided at the side end of the fixed cover plate 202. A round through hole is provided at a position corresponding to the square through hole in the middle of the fixed frame 201 on the end face of the rotating shaft 1502. The high-speed chain disk control key 1504 is a square block, one end of which is provided with a protrusion 3, and the other end of the same side is provided with a circular column 4. The end face of the protrusion 3 is Inclined surface, a circular hole is provided on the end of the high-speed chain disk control key 1504 opposite to the circular column 4, and a third spring 7 is arranged in the circular hole. The medium-speed chain disk control key 1503 is an L-shaped plate, a circular hole is provided on one end thereof, and a second spring 6 is arranged in the circular hole. A groove 5 is provided on the end face of the other side of the L-shape. The high-speed chain disk control key 1504 is movably connected to the square through hole in the middle of the fixed frame 201 through the third spring 7, and the circular column 4 at its end passes through the circular through hole on the rotating shaft 1502.

[0037] The medium-speed chain wheel control key 1503 controls the medium-speed chain wheel 13, which is connected in the chute on the side wall of the rotating shaft 1502 through the second spring 6. When shifting to the medium-speed gear, the medium-speed chain wheel control key 1503 is displaced under force and moves to engage with the helical teeth of the ring shaft 16 of the medium-speed chain wheel 13. The crank 15 rotates to drive the medium-speed chain wheel 13 to rotate and thus operate at medium speed; the high-speed chain wheel control key 1504 controls the high-speed chain wheel 14. The high-speed chain wheel control key 1504 is a square block, with a protrusion 3 at one end and a circular column 4 at the other end on the same side. The end face of the protrusion 3 is an inclined surface, and the circular column 4 penetrates through the rotating shaft 1502 and extends out. When shifting to the high-speed gear, under the action of the third spring 7, the protrusion 3 below the high-speed chain wheel control key 1504 engages with the helical teeth of the ring shaft 16 of the high-speed chain wheel 14, and the crank 15 rotates to drive the high-speed chain wheel 14 to rotate and thus operate at high speed.

[0038] Preferably, as Figures 1-3 shown, the shifting mechanism includes a first turntable 8 and a second turntable 9, and the second turntable 9 is rotatably connected to the first turntable 8;

[0039] The first turntable 8 is provided with a medium-speed guide groove 801 and a high-speed guide groove 807. The medium-speed guide groove 801 and the high-speed guide groove 807 are provided with V-shaped limit blocks 802. The V-shaped limit blocks 802 are connected in the grooves through pins 803. The V-shaped limit blocks 802 can rotate in the grooves. The bottom of the pin 803 is connected with a return spring to limit the rotation of the V-shaped limit blocks 802. At least one side of the medium-speed guide groove 801 and the high-speed guide groove 807 is connected with a return pull spring 804, and the other end of the return pull spring 804 is connected to the second turntable 9. The first turntable 8 is provided with a medium-speed small bearing 805 and a high-speed small bearing 806;

[0040] The second turntable 9 is provided with a medium-speed rotating rod 901 and a high-speed rotating rod 906. One end of the medium-speed rotating rod 901 and the high-speed rotating rod 906 is rotatably connected to the second turntable 9, and the other end is provided with a support rod 902. The support rod 902 extends into the medium-speed guide groove 801 and the high-speed guide groove 807 and can slide in the grooves. The middle parts of the medium-speed rotating rod 901 and the high-speed rotating rod 906 are connected with a limit spring 903 to always lean towards the center of the second turntable 9. A first relief groove 904 and a second relief groove 905 are opened in the middle of the second turntable 9, and an adjustment assembly 100 is provided at the first relief groove 904.

[0041] The rotation of the second turntable 9 drives the medium-speed rotating rod 901, the high-speed rotating rod 906 and the support rod 902 to move along the medium-speed guiding groove 801 and the high-speed guiding groove 807. Under the action of the limiting spring 903, the medium-speed rotating rod 901 and the high-speed rotating rod 906 always lean towards the center of the turntable. The support rod 902 moves in the groove and is restricted when it reaches the V-shaped limiting block 802 and is stuck in the concave cavity of the V-shaped limiting block 802. The V-shaped limiting block 802 also rebounds to the initial position under the restriction of the return spring at the bottom of the pin 803. The return pull spring 804 drives the second turntable 9 back to the initial position.

[0042] Preferably, as Figure 4 shown, the adjusting assembly 100 includes an adjusting rod 1001, a connecting plate 1002, and a pulling plate 1003. The middle part of the adjusting rod 1001 is rotatably connected to the connecting plate 1002, and the end of the adjusting rod 1001 is fixedly connected to the pulling plate 1003. The connecting plate 1002 is fixed on the second turntable 9, and the pulling plate 1003 is connected to the second turntable 9 by a spring. The adjusting assembly 100 is used to control the high-speed chain disk control key 1504. The adjusting rod 1001 contacts the circular column 4 of the high-speed chain disk control key 1504. When the adjusting rod 1001 tilts up, it pushes out the circular column 4, and the protrusion 3 below the high-speed chain disk control key 1504 disengages from the helical teeth of the circular ring shaft 16 of the high-speed chain disk 14.

[0043] Preferably, as Figure 7 shown, a medium-speed pressure variable member 1201 and a high-speed pressure variable member 1203 are connected to the low-speed chain disk 12 through a movable shaft. A pressure rod 1202 is provided on the medium-speed pressure variable member 1201. The pressure rod 1202 can be pressed into the groove 5 of the medium-speed chain disk control key 1503 as the medium-speed pressure variable member 1201 rotates. The high-speed pressure variable member 1203 contacts the adjusting rod 1001 of the adjusting assembly 100. When shifting to the medium-speed gear, the medium-speed small bearing 805 on the shift disk 1 presses on the medium-speed pressure variable member 1201, and the pressure rod 1202 is pressed into the groove 5 of the medium-speed chain disk control key 1503 as the medium-speed pressure variable member 1201 is pressured, controlling the medium-speed chain disk control key 1503 to push inward so that it engages with the helical teeth of the circular ring shaft 16; when shifting to the high-speed gear, the high-speed small bearing 806 on the shift disk 1 presses on the high-speed pressure variable member 1203, and the high-speed pressure variable member 1203 presses one end of the adjusting rod 1001, and the other end of the adjusting rod 1001 gives way to the circular column 4 of the high-speed chain disk control key 1504, so that under the action of the third spring 7, the protrusion 3 below the high-speed chain disk control key 1504 engages with the helical teeth of the circular ring shaft 16 of the high-speed chain disk 14.

[0044] Preferably, as Figure 8 、 9 、10 shown, the middle parts of the medium-speed chain disk 13 and the high-speed chain disk 14 are provided with coaxial circular ring shafts 16, and the end faces of the circular ring shafts 16 are provided with helical teeth. The helical teeth allow the control key to disengage at any time and can engage again under the action of the spring.

[0045] Preferably, the widths of the medium-speed chain disc control key 1503 and the high-speed chain disc control key 1504 are the same.

[0046] Preferably, washers are provided between the shift plate 1 , the low-speed chain plate 12 , the medium-speed chain plate 13 , and the high-speed chain plate 14 , respectively.

[0047] Another object of the present invention is to provide a bicycle comprising the above bicycle three-speed transmission.

[0048] Working process and principle:

[0049] The low, medium and high speed chain discs are installed, the crank 15 is fixedly connected to the low speed chain disc 12 and the second turntable 9, the crank 15 is connected to the medium and high speed chain discs through bearings, the first turntable 8 is rotatably connected to the second turntable 9 to form an integral shift disc 1; the starting gear is the low speed gear, there is no control of the shift disc 1, except for the medium speed and high speed chain discs, all other components rotate with the crank 15, the medium speed chain disc 13 and the high speed chain disc 14 are still in a stationary state, when changing to the medium speed gear, twist the speed regulator on the handle, the speed change plate is in frictional contact with the outer ring of the shift disc 1, and the outer ring of the shift disc 1, i.e. the first turntable 8, is restricted from rotating. 8 and the second turntable 9 produce relative rotation, the medium-speed rotating rod 901 of the second turntable 9 moves along the medium-speed guide groove 801 and is restricted in the concave cavity of the V-shaped limit block 802. At this time, the medium-speed small bearing 805 of the first turntable 8 is just pressed on the medium-speed pressure-changing piece 1201 of the low-speed chain disc 12, so that the pressure rod 1202 on the medium-speed pressure-changing piece 1201 is pressed into the groove 5 of the medium-speed chain disc control key 1503, so that the medium-speed chain disc control key 1503 is matched with the helical teeth of the circular shaft 16 of the medium-speed chain disc 13. At this time, the low-speed chain disc 12 and the medium-speed chain disc 13 rotate synchronously, and the high-speed chain disc 14 is in a stationary state.

[0050] When changing to high gear, twist the speed regulator on the handle again, the speed change plate and the outer ring of the shift plate 1 frictionally contact, the second turntable 9 and the first turntable 8 produce relative rotation, the high-speed rotating rod 906 of the second turntable 9 moves along the high-speed guide groove 807, moves to the concave cavity of the V-shaped limit block 802 and is restricted. At this time, the high-speed small bearing 806 of the first turntable 8 is pressed on the high-speed pressure-changing piece 1203 of the low-speed chain disc 12, and the high-speed pressure-changing piece 1203 is pressed on the end of the adjusting rod 1001 close to the spring, so that the other end of the adjusting rod 1001 is rotated into the first give way groove 904 of the second turntable 9, so that the high-speed chain disc control key 1504 is engaged with the helical teeth of the annular shaft 16 of the high-speed chain disc 14 under the action of the third spring 7. At this time, although the low, medium and high speed chain discs are running at the same time, the low speed chain disc 12 and the medium speed chain disc 13 are actually idling.

[0051] For high-speed to low-speed adjustment, turn the speed governor on the handgrip. The variable-speed piece makes frictional contact with the outer ring of the shift disc 1. The high-speed rotating rod 906 disengages from the V-shaped limit block 802. The return tension spring 804 pulls the first turntable 8 back to the starting position. The high-speed small bearing 806 separates from the high-speed pressure-variable part 1203. At the same time, the medium-speed small bearing 805 also separates from the medium-speed pressure-variable part 1201. The crank 15 stops rotating for one second, allowing the helical teeth of the ring shaft 16 of the high-speed chain sprocket 14 to disengage from the high-speed chain sprocket control key 1504, and the helical teeth of the ring shaft 16 of the medium-speed chain sprocket 13 also disengage from the medium-speed chain sprocket control key 1503. Then the vehicle runs at a low speed.

[0052] The inclination direction of the helical teeth of the ring shaft 16 can be adjusted as needed. To protect the whole device, a protective housing can also be added outside it. The medium-speed chain sprocket 13 and the high-speed chain sprocket 14 can also be separately installed with the shift disc 1 and the low-speed chain sprocket 12.

[0053] In summary, in the present invention, the low-speed chain sprocket 12, the medium-speed chain sprocket 13, and the high-speed chain sprocket 14 respectively connect to drive their respective chains, and the shift disc 1 is used to control the gear shift, achieving smooth and easy 360-degree gear shifting without dead angles, without causing the chain to be deflected and derailed. Moreover, the internal parts are all realized through mechanical structures, without involving any electronic devices, with low production and manufacturing costs, and the relevant components of the existing bicycle can be replaced as a whole.

[0054] Only some exemplary embodiments of the present invention have been described by way of illustration. Undoubtedly, for those of ordinary skill in the art, without departing from the spirit and scope of the present invention, the described embodiments can be modified in various different ways. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A three-speed bicycle transmission, comprising a speed regulator provided on the handlebar and a speed-changing piece on the vehicle body, the speed regulator and the speed-changing piece being connected by a speed-changing wire, characterized in that: It includes a three-stage transmission. The three-stage transmission includes a shift disk (1), a low-speed chain disk (12), a medium-speed chain disk (13), a high-speed chain disk (14) and a crank (15) which are combined in sequence. The low-speed chain disk (12) is fixedly connected to the crank (15). The medium-speed chain disk (13) and the high-speed chain disk (14) are connected to the crank (15) through bearings. The low-speed chain disk (12), the medium-speed chain disk (13) and the high-speed chain disk (14) are respectively connected with a chain alone. A linkage mechanism is provided on the crank (15), and a shifting mechanism is provided on the shift disk (1). The medium-speed chain disk (13) and the high-speed chain disk (14) are controlled by the interaction between the shifting mechanism on the shift disk (1) and the linkage mechanism on the crank (15). The shift disk (1) is in contact connection with the shift piece; The linkage mechanism includes a crank arm (1501), a rotating shaft (1502), a medium-speed chain disk control key (1503), and a high-speed chain disk control key (1504). The crank arm (1501) and the rotating shaft (1502) are fixedly connected. The high-speed chain disk control key (1504) is connected to the end of the crank arm (1501) through a limiting component (2). A chute is opened on the side wall of the rotating shaft (1502), and the medium-speed chain disk control key (1503) is connected in the chute on the side wall of the rotating shaft (1502) through a second spring (6).

2. The three-speed bicycle transmission according to claim 1, characterized in that: The limiting component (2) includes a fixed frame (201) and a fixed cover plate (202). The middle part of the fixed frame (201) is a square through hole. A screw hole is opened at the end of the fixed frame (201). A corresponding through hole is opened at the side end of the fixed cover plate (202). A circular through hole is opened at the position on the end face of the rotating shaft (1502) corresponding to the square through hole in the middle of the fixed frame (201). The high-speed chain disk control key (1504) is a square block, with a protrusion (3) at one end and a circular column (4) at the other end on the same side. The end face of the protrusion (3) is an inclined surface. A round hole is opened at the end of the high-speed chain disk control key (1504) opposite to the circular column (4). A third spring (7) is arranged in the round hole. The medium-speed chain disk control key (1503) is an L-shaped plate, with a round hole opened at one end, and the second spring (6) is arranged in the round hole. A groove (5) is arranged on the end face of the other side of the L shape. The high-speed chain disk control key (1504) is movably connected in the square through hole in the middle of the fixed frame (201) through the third spring (7), and the circular column (4) at its end penetrates through the circular through hole on the rotating shaft (1502).

3. The three-speed bicycle transmission according to claim 2, characterized in that: The shifting mechanism includes a first turntable (8) and a second turntable (9). The second turntable (9) is rotatably connected to the first turntable (8); The first turntable (8) is provided with a medium-speed guiding groove (801) and a high-speed guiding groove (807). The medium-speed guiding groove (801) and the high-speed guiding groove (807) are provided with V-shaped limit blocks (802). The V-shaped limit blocks (802) are connected in the grooves by pins (803). The V-shaped limit blocks (802) can rotate in the grooves. The bottom of the pins (803) is connected with a return spring to limit the rotation of the V-shaped limit blocks (802). At least one side of the medium-speed guiding groove (801) and the high-speed guiding groove (807) is connected with a return pull spring (804). The other end of the return pull spring (804) is connected to the second turntable (9). The first turntable (8) is provided with a medium-speed small bearing (805) and a high-speed small bearing (806); The second turntable (9) is provided with a medium-speed rotating rod (901) and a high-speed rotating rod (906). One end of the medium-speed rotating rod (901) and the high-speed rotating rod (906) is rotatably connected to the second turntable (9), and the other end is provided with a support rod (902). The support rod (902) extends into the medium-speed guiding groove (801) and the high-speed guiding groove (807) and can slide in the grooves. The middle parts of the medium-speed rotating rod (901) and the high-speed rotating rod (906) are connected with a limit spring (903) to always lean towards the center of the second turntable (9). A first relief groove (904) and a second relief groove (905) are formed in the middle of the second turntable (9). An adjusting assembly (100) is provided at the first relief groove (904).

4. The three-speed bicycle transmission according to claim 3, characterized in that: The adjusting assembly (100) includes an adjusting rod (1001), a connecting plate (1002), and a pulling plate (1003). The middle part of the adjusting rod (1001) is rotatably connected to the connecting plate (1002). The end of the adjusting rod (1001) is fixedly connected to the pulling plate (1003). The connecting plate (1002) is fixed on the second turntable (9). The pulling plate (1003) is connected to the second turntable (9) by a spring.

5. The three-speed bicycle transmission according to claim 4, characterized in that: A medium-speed pressure change member (1201) and a high-speed pressure change member (1203) are connected to the low-speed chain wheel (12) by a movable shaft. A pressure rod (1202) is provided on the medium-speed pressure change member (1201). The pressure rod (1202) can be pressed into the groove (5) of the medium-speed chain wheel control key (1503) as the medium-speed pressure change member (1201) rotates. The high-speed pressure change member (1203) contacts the adjusting rod (1001) of the adjusting assembly (100).

6. The three-speed bicycle transmission according to claim 1, characterized in that: Coaxial circular ring shafts (16) are provided in the middle of the medium-speed chain wheel (13) and the high-speed chain wheel (14). The end faces of the circular ring shafts (16) are provided with helical teeth.

7. The three-speed bicycle transmission according to claim 1, characterized in that: The medium-speed chain wheel control key (1503) and the high-speed chain wheel control key (1504) have the same width.

8. The three-speed bicycle transmission according to any one of claims 1-7, characterized in that: Washers are respectively provided between the shift disc (1), the low-speed chain wheel (12), the medium-speed chain wheel (13), and the high-speed chain wheel (14).

9. A bicycle, characterized in that: It includes a three-speed bicycle transmission as described in any one of claims 1-8.

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