CN108945262B

CN108945262B - City bicycle

Info

Publication number: CN108945262B
Application number: CN201810638296.8A
Authority: CN
Inventors: 易志国
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-06-20
Filing date: 2018-06-20
Publication date: 2020-08-14
Anticipated expiration: 2038-06-20
Also published as: CN108945262A

Abstract

A city bicycle comprises a frame, wherein the frame is provided with a front wheel and a rear wheel and comprises a supporting tube, a sliding rod is arranged in the supporting tube in a sliding mode, a saddle is arranged at the end part of the sliding rod, and an energy storage part is arranged in the supporting tube; a rack is arranged on the sliding rod, a transmission support is arranged on the supporting tube, a driving shaft and a driven shaft are arranged on the transmission support, a first gear meshed with the rack is arranged on the driving shaft, a second gear connected with the first gear is arranged on the driven shaft, and the second gear comprises a ratchet wheel and pawl assembly connected with the driven shaft; the second gear is connected with a driving chain wheel, and the rear wheel is connected with a driven chain wheel; the stay tube is provided with and supports pedal, and the outside of stay tube is provided with the slide, and the top of slide is provided with the guide wheel, and the one end and the slide bar of stay cord are connected, and the other end is connected with supporting pedal, and the power that the gravity through people self went as the bicycle reduces the people physical demands when riding the bicycle, increases the interest of the in-process of riding simultaneously.

Description

City bicycle

Technical Field

The invention relates to a bicycle, in particular to an urban bicycle.

Background

Bicycles, also known as bicycles or bicycles, are typically two-wheeled small land vehicles. After a person rides the vehicle, the person steps on the pedal as power, and the vehicle is a green and environment-friendly vehicle. The bicycle is used as an environment-friendly vehicle for riding instead of walking and going out; more and more people use bicycles as fitness equipment for riding exercise and bicycle touring.

At present, the drive system of a bicycle: it is composed of pedal, central axle, toothed disc, crank, chain, flywheel, back axle and back wheel. The driving force is from the pedaling force of the feet of the person, and the pedals are driven by a crank, a chain wheel, a chain, a flywheel, a rear shaft and other parts, so that the bicycle continuously moves forwards.

The existing bicycle depends on muscle strength of legs of a person in the running process, the legs of the person can consume a large amount of energy in the long-time riding process to cause the legs to have ache, and the prior art has an improvement.

Disclosure of Invention

In order to solve the technical problems, the invention provides the urban bicycle, the sliding rod is pushed to slide in the supporting tube by the gravity of a person, the driving chain wheel drives the driven chain wheel to rotate through the chain by the aid of a transmission part arranged on the transmission mechanism, the gravity of the person is used as the driving power of the bicycle, physical consumption of the person during riding the bicycle is reduced, and meanwhile, interestingness in the riding process is increased.

In order to achieve the purpose, the technical scheme of the invention is as follows: a city bicycle comprises a frame, wherein a front wheel and a rear wheel are rotatably arranged on the frame, the frame comprises a supporting tube which is arranged along the vertical direction, a sliding rod is arranged in the supporting tube in a sliding manner, a saddle is arranged at the end part of the sliding rod, one side of the sliding rod, which is far away from the saddle, is arranged in the supporting tube, and an energy storage part connected with a supporting rod is arranged in the supporting tube; the sliding rod is provided with a rack extending along the length direction of the sliding rod, the supporting tube is provided with a transmission support, the transmission support is provided with a transmission mechanism, the transmission support is provided with a driving shaft and a driven shaft, the transmission mechanism comprises a first gear which is arranged on the driving shaft and meshed with the rack, the driven shaft is provided with a second gear connected with the first gear, and the second gear comprises a ratchet and pawl assembly connected with the driven shaft; the second gear is connected with a driving chain wheel, a driven chain wheel connected with a rear wheel is arranged on the frame, and a chain is sleeved between the driving chain wheel and the driven chain wheel; one side of the supporting tube, which is far away from the saddle, is provided with a supporting pedal, the outer side of the supporting tube is provided with a slide way, the supporting pedal is arranged on the slide way in a sliding manner, a guide wheel is arranged above the slide way, a pull rope is connected onto the guide wheel, one end of the pull rope is connected with one end, which is far away from the saddle, of the sliding rod, and the other end of the pull rope is connected with the supporting pedal.

By adopting the technical scheme, when a person rides a bicycle, the feet of the person tread on the supporting foot pedals, the buttocks are seated on the saddle, the sliding rod moves towards one side of the saddle under the action of the guide wheel by the stay cord when the feet of the person exert force, then the feet of the user leave the supporting pedals, and gravity is exerted on the sliding rod through the buttocks of the person, so that the sliding rod moves towards the side far away from the saddle; on the other hand, the energy generated when the sliding rod slides is stored in the energy storage element; the saddle is located the minimum after, and people's foot is placed once more on the supporting legs is stepped on, then the buttock leaves the saddle, tramples through self gravity and supports pedal, makes and supports pedal towards saddle one side motion, makes the slide bar move towards the one side of keeping away from the saddle through the stay cord, and the power that the bicycle went is regarded as to gravity through people self, reduces the physical demands when people ride the bicycle, increases the interest of the in-process of riding simultaneously.

The invention is further configured to: still be provided with adjusting gear on the driven shaft, still be provided with on the driving shaft and be used for with adjusting gear complex third gear, adjusting gear slides and sets up on the driven shaft, adjusting gear is including fourth gear and the fifth gear of diameter difference, the diameter of fourth gear is less than the fifth gear, through the meshing transmission between first gear and fourth gear or third gear and the fifth gear between driving shaft and the driven shaft.

Through adopting above-mentioned technical scheme, the adjusting gear who sets up on through the driven shaft changes the drive ratio between driven shaft and the driving shaft to the user selects suitable drive ratio according to the topography of riding of reality, improves the comfort level of city bicycle in-process of riding.

The invention is further configured to: an annular groove is formed in the fifth gear, the section of the annular groove is L-shaped, an L-shaped pull rod is arranged in the annular groove, and the adjusting gear slides on the driven shaft after the pull rod is pulled.

By adopting the technical scheme, the pull rod is connected with the fifth gear through the annular groove, the annular groove of the fifth gear rotates along with the fifth gear in the rotating process, the interference between the pull rod and the fifth gear is avoided, and the adjusting gear slides on the driven shaft after the pull rod is pulled, so that the adjustment between gears with different transmission ratios is realized, and people can conveniently switch through the pull rod in the riding process.

The invention is further configured to: the transmission support is provided with a transition shaft, the transition shaft is provided with a sixth gear meshed with the second gear, and the driving sprocket is arranged on the transition shaft and is coaxial with the sixth gear.

By adopting the technical scheme, the driving chain wheel is arranged on the transition shaft, the sixth gear and the second gear are meshed to enable the transition shaft to rotate so as to drive the driving chain wheel to rotate, the transition shaft separates the driving chain wheel from the adjusting gear, people are prevented from blocking and stopping the bicycle by adjusting the transmission ratio through the adjusting gear, and the flow performance of the bicycle in the running process is improved.

The invention is further configured to: the transmission support is provided with a speed reducing shaft, the speed reducing shaft is provided with a seventh gear meshed with the sixth gear and a friction disc for reducing speed, the transmission support is provided with a friction wheel opposite to the friction disc, the friction wheel is arranged in a sliding mode along the length direction of the speed reducing shaft, and the friction wheel is connected with a control mechanism for controlling the friction wheel to slide.

Through adopting above-mentioned technical scheme, meshing between sixth gear and the seventh gear through the friction between friction pulley and the friction disk, makes the rotation of sixth gear receive the resistance to make drive sprocket's rotation receive the resistance, and then reduce city bicycle's the speed of traveling.

The invention is further configured to: the speed reducing shaft is provided with a cylindrical bearing, and the friction disc is rotatably arranged on the speed reducing shaft through the cylindrical bearing.

Through adopting above-mentioned technical scheme, cylindrical bearing makes friction disc and reduction shaft separation, moves towards friction pulley one side and along with the reduction shaft rotation after the friction disc with the friction pulley butt to make drive sprocket's rotation receive the resistance, cylindrical bearing makes the friction pulley intermittent type rotate, prolongs the life of friction disc.

The invention is further configured to: the friction disc further comprises an eighth gear meshed with the rack.

Through adopting above-mentioned technical scheme, the friction disk is last set up with the eighth gear of rack toothing, after friction disk and friction wheel butt, the friction disk rotates along with the reduction shaft, and the energy conversion when rotating the transition shaft through the meshing action between eighth gear and the rack is the motion of rack, converts the energy of braking consumption into the potential energy of slide bar or stores in the energy storage piece, and the restart or the acceleration after the city bicycle braking of being convenient for.

The invention is further configured to: the supporting tube comprises a channel for the sliding rod to slide, and a plurality of groups of sliding components for reducing friction force are distributed in the channel along the length direction of the supporting tube.

Through adopting above-mentioned technical scheme, improve the smooth nature of slide bar reciprocating motion in the bracing piece through sliding assembly, avoid the slide bar card to die in the bracing pipe.

The invention is further configured to: the sliding assembly comprises a bearing or a ball which is arranged in the channel and is abutted against the sliding rod, and the bearing or the ball is distributed on the peripheral side of the sliding rod.

Through adopting above-mentioned technical scheme, the butt through bearing or ball makes the slide bar roll and sets up in the stay tube, reduces the frictional force between stay tube and the slide bar, only need paint the lubrication on the slide bar can make lubricating oil evenly paint on the bearing or the ball in the stay tube when maintaining simultaneously, the maintenance of the city bicycle of being convenient for.

The invention is further configured to: the energy storage part is an extension spring arranged in the support pipe, and the extension spring pulls the sliding rod to move towards the side far away from the saddle.

Through adopting above-mentioned technical scheme, extension spring pulling slide bar is towards keeping away from saddle one side motion, makes to support the middle part that the pedal is located the slide, and the people can trample in the slide bottom with supporting the pedal when getting on the bus, and the people utilizes self gravity to promote the saddle downstream after getting on the bus and can make the bicycle travel, the start of the city bicycle of being convenient for.

In summary, the present invention has the following effects:

1. the city bicycle shortens the transmission lever of the pedal type bicycle, and is convenient for a rider to use;

2. the driving force of the city bicycle when the city bicycle runs is converted by the gravity of a person, so that the cruising ability of the city bicycle is greatly improved;

3. the energy during braking is stored by the potential energy of the sliding rod and the contraction of the extension spring, so that the city bicycle can be restarted or accelerated after being braked;

4. greatly improving the fun of people when riding the bicycle.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the embodiments or the description of the prior art will be briefly described below.

FIG. 1 is a schematic view of the overall structure of a city bicycle;

FIG. 2 is a schematic view showing the internal structure of the support tube and the slide bar;

FIG. 3 is a schematic cross-sectional view of a support tube, primarily for embodying a sliding assembly within the support tube;

FIG. 4 is a schematic view of the overall structure of the transmission bracket and the transmission mechanism;

fig. 5 is a schematic view of the overall structure of the slide bar.

In the figure: 1. a frame; 11. supporting a tube; 111 a channel; 12. a transmission bracket; 121. a drive shaft; 122. a driven shaft; 123. A transition shaft; 124. a deceleration shaft; 125. a pull rod; 13. a slideway; 14. supporting the pedals; 15. a guide wheel; 16. pulling a rope; 2. a front wheel; 3. a rear wheel; 4. a slide bar; 41. a rack; 5. a vehicle seat; 6. an extension spring; 7. a transmission mechanism; 71. A first gear; 72. a second gear; 73. a third gear; 74. a fourth gear; 75. a fifth gear; 751. an annular groove; 76. a sixth gear; 77. a seventh gear; 8. a sprocket assembly; 81. a drive sprocket; 82. a driven sprocket; 83. a chain; 9. a brake assembly; 91. a friction wheel; 92. a friction disk; 93. a cylindrical bearing; 94. an eighth gear; 10. a sliding assembly; 101. a bearing; 21. a control mechanism; 211. a sleeve; 2111. a guide wire; 212. a butting block; 2121. connecting columns; 213. A thrust ball bearing; 214. a torsion spring.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings.

As shown in fig. 1 to 5, a city bicycle comprises a frame 1, a front wheel 2 and a rear wheel 3 are respectively rotatably arranged on the front side and the rear side of the frame 1, the frame 1 comprises a support tube 11 arranged along the vertical direction, the support tube 11 is arranged in a hollow manner, a sliding rod 4 is arranged in the support tube 11 in a sliding manner, a seat 5 is arranged at the end part of the sliding rod 4, one side of the sliding rod 4 far away from the seat 5 is inserted into the support tube 11, an energy storage part for absorbing redundant energy is also arranged in the support tube 11, the energy storage part is an extension spring 6 for connecting the sliding rod 4 with the support tube 11, and the extension spring 6 enables the sliding rod 4 to move towards the side far away from the; the sliding rod 4 is provided with a rack 41 extending along the length direction of the sliding rod, the supporting tube 11 is provided with a transmission support 12, the transmission support 12 is provided with a transmission mechanism 7 for converting the reciprocating motion of the rack 41 into rotation, the transmission mechanism 7 comprises a driving shaft 121 and a driven shaft 122 which are rotatably arranged on the transmission support 12, the driving shaft 121 is provided with a first gear 71 meshed with the rack 41, the first gear 71 and the driving shaft 121 are in fit connection with a key groove through a key, the driven shaft 122 is provided with a second gear 72 connected with the first gear 71, the second gear 72 comprises a ratchet and pawl assembly connected with the driven shaft 122, the ratchet and pawl assembly enables the second gear 72 to drive the driven shaft 122 to rotate only in one direction, and the rotation of the driven shaft 122 is prevented from being influenced when the first gear 71 rotates reversely; the second gear 72 is connected with a driving sprocket 81, a driven sprocket 82 connected with the rear wheel 3 is arranged on the frame 1, a chain 83 is sleeved between the driving sprocket 81 and the driven sprocket 82, the driven sprocket 82 is driven to rotate by the rotation of the driving sprocket 81, so that the reciprocating motion of the rack 41 is converted into the rotation of the rear wheel 3, and the bicycle runs; a supporting pedal 14 is arranged on one side of the supporting pipe 11 far away from the saddle 5, a slideway 13 is arranged on the outer side of the supporting pipe 11, the supporting pedal 14 is arranged on the slideway 13 in a sliding way, a guide wheel 15 is arranged above the slideway 13, a pull rope 16 is connected on the guide wheel 15, one end of the pull rope 16 is connected with one end of the sliding rod 4 far away from the saddle 5, the other end of the pull rope 16 is connected with the supporting pedal 14, when the foot of a person steps on the supporting pedal 14, the sliding rod 4 slides towards one side of the saddle 5 through the pull rope 16, and the sliding rod 4 has a downward sliding stroke.

In order to facilitate a user to adjust the transmission ratio of the transmission mechanism 7 in the riding process, the driven shaft 122 is further provided with an adjusting gear, the driving shaft 121 is provided with a third gear 73 used for being matched with the adjusting gear, the adjusting gear is arranged on the driven shaft 122 in a sliding manner, the adjusting gear comprises a fourth gear 74 and a fifth gear 75 which are different in diameter, the diameter of the fourth gear 74 is smaller than that of the fifth gear 75, and the driving shaft 121 and the driven shaft 122 are in meshing transmission through the first gear 71 and the fourth gear 74 or the third gear 73 and the fifth gear 75; an annular groove 751 is formed in the fifth gear 75, the section of the annular groove 751 is arranged in an L shape, an L-shaped pull rod 125 is arranged in the annular groove 751, the pull rod 125 is slidably arranged on the transmission support 12 and arranged along the axial direction of the driven shaft 122, the adjustment gear slides on the driven shaft 122 after the pull rod 125 is pulled to realize the switching between the first gear 71 and the fourth gear 74, and the third gear 73 and the fifth gear 75, and in the scheme, the fourth gear 74 and the fifth gear 75 are integrally formed and arranged on the driven shaft 122 through splines.

In order to improve the stability of the city bicycle during running, the transmission bracket 12 is provided with a transition shaft 123, the transition shaft 123 is provided with a sixth gear 76 engaged with the second gear 72, and the driving sprocket 81 is arranged on the transition shaft 123 and is coaxial with the sixth gear 76.

Furthermore, the invention also provides a brake assembly 9 for reducing the speed of a city bicycle, a speed reducing shaft 124 is arranged on a transmission bracket 12, a seventh gear 77 meshed with a sixth gear 76 and a friction disc 92 for reducing the speed are arranged on the speed reducing shaft 124, a friction wheel 91 opposite to the friction disc 92 is arranged on the transmission bracket 12, the friction wheel 91 is arranged in a sliding way along the length direction of the speed reducing shaft 124, the friction wheel 91 is connected with a control mechanism 21 for controlling the friction wheel 91 to slide, the control mechanism 21 comprises a sleeve 211 fixedly arranged on the transmission bracket 12, the speed reducing shaft 124 penetrates through the sleeve 211, a guide wire 2111 with a thread structure is arranged on the outer side of the sleeve 211, an abutting block 212 is rotatably connected on the outer side of the sleeve 211 through a guide wire 2111, the abutting block 212 is fixedly connected with the friction wheel 91, a connecting post 2121 for pulling a brake cable extends on the abutting block 212, a person pulls the brake cable in the riding process to rotate the abutting block 212 through the connecting post 2121, the contact block 212 pushes the friction wheel 91 to slide on the speed reducing shaft 124 through the action of the guide wire 2111, a torsion spring 214 is further arranged between the contact block 212 and the transmission bracket 12 for facilitating the reset of the contact block 212, and the contact block 212 is reset through rotating on the sleeve 211 under the action of the torsion spring 214; in the scheme, the friction wheel 91 is arranged on the speed reducing shaft 124 through a spline; in order to increase the load carrying capacity of the friction wheel 91, a thrust ball bearing 213 is provided on the side of the abutment block 212 remote from the transmission support 12, and the friction wheel 91 is arranged on the abutment block 212 via the thrust ball bearing 213.

In order to prolong the service life of the friction disc 92, a cylindrical bearing 93 is arranged on the speed reducing shaft 124, and the friction disc 92 is rotatably arranged on the speed reducing shaft 124 through the cylindrical bearing 93; in order to collect and utilize the kinetic energy of the bicycle during braking, the friction disc 92 further comprises an eighth gear 94 engaged with the rack 41; when the bicycle runs, the seventh gear 77 is meshed with the sixth gear 76 so as to enable the speed reducing shaft 124 to rotate, and the friction disc 92 is separated from the speed reducing shaft 124 under the action of the cylindrical bearing 93, so that the problem that the friction disc 92 interferes with the rack 41 in the riding process of the city bicycle is solved; when the bicycle is decelerated, the abutment block 212 rotates on the sleeve 211, so that the abutment block 212 pushes the friction wheel 91 to move toward the friction disc 92 and abuts against the friction disc 92, the friction disc 92 rotates along with the deceleration shaft 124 after the friction wheel 91 abuts against the friction disc 92, the slide rod 4 slides by the meshing action of the eighth gear 94 and the rack 41, and energy during deceleration is stored in the extension spring 6.

In order to improve the stability of the sliding rod 4 sliding in the support tube 11, the support tube 11 includes a channel 111 for the sliding rod 4 to slide, a plurality of sets of sliding assemblies 10 for reducing friction are disposed in the channel 111 along the length direction of the support tube 11, the sliding assemblies 10 include a bearing 101 or balls disposed in the channel 111 and abutting against the sliding rod 4, and the bearing 101 or balls are disposed on the peripheral side of the sliding rod 4.

The gear and the shaft which are not specially explained in the scheme are matched in a mode of a key and a key groove.

The specific implementation process comprises the following steps:

when a person rides the bicycle, the feet of the person step on the supporting pedals 14, the buttocks are seated on the seat 5, when the feet of the person exert force, the pull rope 16 enables the sliding rod 4 to move towards one side of the seat 5 under the action of the guide wheel 15, then the feet of the user leave the supporting pedals 14, gravity is exerted on the sliding rod 4 through the buttocks of the person, the sliding rod 4 is enabled to move towards the side far away from the seat 5, on one hand, the sliding rod 4 drives the first gear 71 to rotate through the rack 41 when sliding, the first gear 71 drives the driven shaft 122 to rotate through the second gear 72 after rotating, the second gear 72 is arranged on the driven shaft 122 through the ratchet pawl, the driven shaft 122 can only rotate in one direction, the second gear 72 drives the driving chain wheel 81 to rotate after the driven shaft 122 rotates, and the driven chain wheel 82 rotates through the transmission of the chain 83, so that the bicycle starts; on the other hand, the energy generated when the sliding rod 4 slides is stored in the energy storage part; after saddle 5 was located the minimum, people's foot was placed once more on supporting pedal 14, then the buttock leaves saddle 5, tramples through self gravity and supports pedal 14, makes and supports pedal 14 towards saddle 5 one side motion, makes slide bar 4 towards the one side motion of keeping away from saddle 5 through stay cord 16, and the power that traveles is regarded as the bicycle through people's self gravity, reduces the physical demands when people ride the bicycle, increases the interest of the in-process of riding simultaneously.

It should be noted that, for those skilled in the art, various changes and modifications can be made without departing from the inventive concept of the present invention, and these changes and modifications belong to the protection scope of the present invention.

Claims

1. A city bicycle comprises a frame (1), wherein a front wheel (2) and a rear wheel (3) are rotatably arranged on the frame (1), and the city bicycle is characterized in that the frame (1) comprises a support tube (11) arranged along the vertical direction, a sliding rod (4) is arranged in the support tube (11) in a sliding manner, a saddle (5) is arranged at the end part of the sliding rod (4), one side of the sliding rod (4) far away from the saddle (5) is arranged in the support tube (11), and an energy storage part connected with the support rod is arranged in the support tube (11); a rack (41) extending along the length direction of the sliding rod (4) is arranged on the sliding rod, a transmission support (12) is arranged on the support tube (11), a transmission mechanism (7) is arranged on the transmission support (12), a driving shaft (121) and a driven shaft (122) are arranged on the transmission support (12), the transmission mechanism (7) comprises a first gear (71) which is arranged on the driving shaft (121) and is meshed with the rack (41), a second gear (72) which is connected with the first gear (71) is arranged on the driven shaft (122), and the second gear (72) comprises a ratchet and pawl component which is connected with the driven shaft (122); the second gear (72) is connected with a driving chain wheel (81), a driven chain wheel (82) connected with the rear wheel (3) is arranged on the frame (1), and a chain (83) is sleeved between the driving chain wheel (81) and the driven chain wheel (82); a supporting pedal (14) is arranged on one side, away from the saddle (5), of the supporting pipe (11), a slide way (13) is arranged on the outer side of the supporting pipe (11), the supporting pedal (14) is arranged on the slide way (13) in a sliding mode, a guide wheel (15) is arranged above the slide way (13), a pull rope (16) is connected onto the guide wheel (15), one end of the pull rope (16) is connected with one end, away from the saddle (5), of the sliding rod (4), and the other end of the pull rope is connected with the supporting pedal (14); still be provided with adjusting gear on driven shaft (122), still be provided with on driving shaft (121) and be used for with adjusting gear complex third gear (73), adjusting gear slides and sets up on driven shaft (122), adjusting gear is including fourth gear (74) and fifth gear (75) that the diameter is different, the diameter of fourth gear (74) is less than fifth gear (75), through the meshing transmission between first gear (71) and fourth gear (74) or third gear (73) and fifth gear (75) between driving shaft (121) and driven shaft (122).

2. The city bicycle according to claim 1, wherein an annular groove (751) is formed in the fifth gear (75), the annular groove (751) is provided with an L-shaped cross section, an L-shaped pull rod (125) is arranged in the annular groove (751), and the adjusting gear slides on the driven shaft (122) after the pull rod (125) is pulled.

3. A city bicycle according to claim 2, characterized in that the transmission bracket (12) is provided with a transition shaft (123), the transition shaft (123) is provided with a sixth gear (76) engaged with the second gear (72), and the driving sprocket (81) is arranged on the transition shaft (123) and coaxially with the sixth gear (76).

4. The city bicycle according to claim 1, wherein a speed reducing shaft (124) is arranged on the transmission support (12), a seventh gear (77) meshed with the sixth gear (76) and a friction disc (92) for reducing speed are arranged on the speed reducing shaft (124), a friction wheel (91) opposite to the friction disc (92) is arranged on the transmission support (12), the friction wheel (91) is arranged in a sliding mode along the length direction of the speed reducing shaft (124), and a control mechanism (21) for controlling the friction wheel (91) to slide is connected to the friction wheel (91).

5. A city bicycle according to claim 4, characterized in that the speed reducing shaft (124) is provided with a cylindrical bearing (93), and the friction disc (92) is rotatably arranged on the speed reducing shaft (124) through the cylindrical bearing (93).

6. A city bicycle according to claim 4 or 5, characterized in that the friction disc (92) further comprises an eighth gear wheel (94) engaging with the rack (41).

7. A city bike according to claim 1, characterized in that the support tube (11) comprises a channel (111) for the sliding rod (4), and that several sets of sliding assemblies (10) are arranged in the channel (111) along the length of the support tube (11) for reducing friction.

8. Urban bicycle according to claim 7, characterized in that the sliding assembly (10) comprises bearings (101) or balls arranged in the channel (111) and abutting against the sliding rod (4), the bearings (101) or balls being distributed on the peripheral side of the sliding rod (4).

9. A city bike according to claim 1, characterized in that the energy storage member is an elongated spring (6) arranged in a support tube (11), which elongated spring (6) pulls the slide bar (4) towards the side away from the saddle (5).