Vehicle body frame structure and motor-assisted bicycle

Abstract

To enable a driver to easily put his / her foot on the ground when a motor-assisted bicycle traveling at a low speed is stopped.SOLUTION: A body frame structure of a motor-assisted bicycle 1 traveling at a low speed of 20 km / h or less per hour includes a down-tube 3 extending obliquely downward from a head pipe 2 and provided with a horizontal portion 33 extending substantially horizontally rearward from a bent portion 32 at a lower end of a downward extending portion 31. The down-tube 3 is formed of a single frame. Footrest portions 22, 22 locally protruding leftward and rightward are attached to the down-tube 3, in a range from the bent portion 32 to a front side from a rear end of the horizontal portion 33. With respect to a midpoint M of a line segment connecting a front wheel axle 201 and a rear wheel axle 211, the footrest portions 22 are disposed in a range from 20% of a wheelbase H on a front side from the midpoint M to 20% of the wheelbase H on a rear side from the midpoint M.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a body frame structure of a motorized bicycle and a motorized bicycle. [Background technology]

[0002] Conventionally, from the standpoint of ensuring rigidity and stability during high-speed driving, motorized bicycles have adopted a double frame structure as disclosed in Patent Document 1. The vehicle frame structure of Patent Document 1 is composed of a main frame extending from a head pipe, a rear frame extending rearward from the main frame by splitting into two, a pair of left and right down tubes hanging down from the head pipe, lower pipes extending substantially horizontally by bending the down tubes, a center frame rising from the rear end of the lower pipe, and stays connecting the center frame and the rear frame. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4188136 Summary of the Invention [Problem to be solved by the invention]

[0004] By the way, in the case of motorized bicycles that are mainly expected to be driven at low speeds, such as certain motorized bicycles that run at 20 km / h or less, the behavior of the body becomes unstable when traveling at low speeds, so there are many opportunities and frequency of stopping. Therefore, it is desirable for the structure to allow the rider to easily place their feet on the ground.

[0005] However, the double frame structure of conventional motorized bicycles is arranged so that the frame overhangs to the left and right even at the points where the rider's feet touch the ground, such as the down tubes that hang down from the head pipe in a pair on the left and right and the pair of lower pipes that extend rearward almost horizontally from each down tube in Patent Document 1. Therefore, when stopping, the rider needs to place his / her feet on the ground outside the frames that overhang to the left and right, making it difficult for the rider to place his / her feet on the ground.

[0006] The present invention has been proposed in consideration of the above-mentioned problems, and aims to provide a body frame structure and a moped that allow the rider to easily place their feet on the ground when stopping a moped traveling at a low speed. [Means for solving the problem]

[0007] The body frame structure of the present invention is a body frame structure for a motor-driven bicycle that travels at a low speed of 20 km / h or less, and comprises a head pipe to which an operating handlebar is attached, and a down tube that extends diagonally downward from the head pipe and has a horizontal section that extends approximately horizontally rearward from a curved section at the lower end of the downward extension, the down tube is formed from a single frame, and a footrest portion that protrudes locally to the left and right is attached to the down tube in a range from the curved section to the front of the rear end of the horizontal section, and the footrest portion is positioned within a range from 20% of the wheelbase forward of the midpoint of a line segment connecting the front and rear axles to within a range of 20% of the wheelbase rearward of the midpoint, based on the midpoint. According to this, the down tube is formed as a single frame, and a foot rest portion is attached to the down tube in a range from the bent portion to the front of the rear end of the horizontal portion, which protrudes left and right locally, and the foot rest portion is arranged within a range from 20% of the wheel base in front of the midpoint of the line segment connecting the front and rear axles to 20% of the wheel base in rear of the midpoint, based on the midpoint. This allows the rider to easily place his / her feet on the ground on both the left and right sides of the body or in front and behind the foot rest portion, and allows the rider to easily place his / her feet on the ground when the motorized bicycle is stopped. In addition, the length of the horizontal portion near the minimum ground clearance or at the minimum ground clearance that the rider straddles when getting on and off the motorized bicycle can be set long, and even riders such as short people and elderly people can easily straddle the horizontal portion to get on and off the motorized bicycle. In other words, the ease with which the rider straddles the frame and the ease of getting on and off the motorized bicycle can be improved. In addition, the rider can use the horizontal portions in front and behind the foot rest portion as foot rests, for example, and this improves comfort when driving. In addition, by positioning the footrest within a range from 20% of the wheelbase in front of the midpoint of the line segment connecting the front and rear axles to 20% of the wheelbase behind the midpoint, a stable posture can be ensured for the rider of a motorized bicycle traveling at a speed of 20 km / h or less.

[0008] The body frame structure of the present invention is characterized in that a pair of left and right rear stays, which are arranged to expand rearward in a Y-shape when viewed in a plane, are fixed to the rear ends of the horizontal sections, a rear tubular section extending approximately horizontally rearward from the rear stays, the seat stays and the seat rails are arranged to form a frame that is shaped like an inverted Z in side view and protrude to the left and right, a bridge tube is installed between the left seat stay and the right seat stay, and the bridge tube is fixed to the upper end of the rear tube, which has its lower end fixed to the horizontal section and extends diagonally upward toward the rear. According to this, by extending the rear tubular portions of the rear stays, the seat stays and the seat rails to the left and right and supporting them in the left-right direction with a bridge tube, and supporting the Z-shaped frame of the rear tubular portions of the rear stays, the seat stays and the seat rails and the bridge tube with the rear tube, it is possible to increase impact resistance and shock absorption against side collisions and improve the safety of the driver.

[0009] The body frame structure of the present invention is characterized in that each of the rear tubular portions and the seat stays are connected by a bottom bridge that is V-shaped in side view, and each of the seat stays and the seat rails are connected by a top bridge that is V-shaped in side view. This makes it possible to more easily form the Z-shaped frame configuration of the rear tubular portions of the rear stays, the seat stays and the seat rails, thereby improving the manufacturing efficiency of the body frame structure.

[0010] The body frame structure of the present invention is characterized in that the front tubular portion of each of the pair of left and right rear stays is formed in a rectangular cross section, the rear end of the down tube is formed in a rectangular cross section, the front tubular portions of each rear stay are overlapped in the left-right direction and welded to each other and fitted into the rear end of the down tube, and the rear end of the down tube is welded to the overlapped front tubular portions of the rear stays around the entire circumference of the rear end of the down tube. This allows the down tube to be joined to the rear stay while maintaining the outline, improving the sense of unity between the down tube and the rear stay. Also, the weld length can be reduced compared to a shape and configuration in which the left and right rear stays are welded to the down tube one by one with a gap between them, improving manufacturing efficiency while obtaining high rigidity. Also, by fitting the front tubular part of the rear stay into the rear end of the down tube while overlapping it in the left-right direction and welding it to the rear end of the down tube all around, the strength of the joint between the rear stay and the down tube can be increased and water such as rainwater can be more reliably prevented from entering the frame through the joint.

[0011] The body frame structure of the present invention is characterized in that the front tubular portion of each of the pair of left and right rear stays is formed in a rectangular cross section, the rear end of the down tube is formed in a rectangular cross section, the front tubular portions of each rear stay are overlapped in the left-right direction and welded to each other while abutting against the rear end surface of the down tube, and the rear end of the down tube is welded to the overlapped front tubular portions of the rear stays around the entire circumference of the rear end of the down tube. This allows the down tube to be joined to the rear stays while maintaining their outline, improving the sense of unity between the down tube and the rear stays. Also, the weld length can be reduced compared to a shape and configuration in which the left and right rear stays are welded all around the down tube one by one with a gap between them, improving manufacturing efficiency while maintaining high rigidity.

[0012] The moped of the present invention is a moped that travels at a low speed of 20 km / h or less, and comprises a head pipe to which an operating handle is attached, and a down tube that extends diagonally downward from the head pipe and has a horizontal section that extends approximately horizontally rearward from a curved section at the lower end of the downward extension, the down tube being formed from a single frame, and a footrest section that protrudes locally to the left and right is attached to the down tube in a range from the curved section to the front of the rear end of the horizontal section, and the footrest section is positioned within a range from 20% of the wheelbase in front of the midpoint of a line segment connecting the front and rear axles to 20% of the wheelbase behind the midpoint, based on the midpoint. According to this, the down tube is formed as a single frame, and a foot rest portion is attached to the down tube in a range from the bent portion to the front of the rear end of the horizontal portion, which protrudes left and right locally, and the foot rest portion is arranged within a range from 20% of the wheel base in front of the midpoint of the line segment connecting the front and rear axles to 20% of the wheel base in rear of the midpoint, based on the midpoint. This allows the rider to easily place his / her feet on the ground on both the left and right sides of the body or in front and behind the foot rest portion, and allows the rider to easily place his / her feet on the ground when the motorized bicycle is stopped. In addition, the length of the horizontal portion near the minimum ground clearance or at the minimum ground clearance that the rider straddles when getting on and off the motorized bicycle can be set long, and even riders such as short people and elderly people can easily straddle the horizontal portion to get on and off the motorized bicycle. In other words, the ease with which the rider straddles the frame and the ease of getting on and off the motorized bicycle can be improved. In addition, the rider can use the horizontal portions in front and behind the foot rest portion as foot rests, for example, and this improves comfort when driving. In addition, by positioning the footrest within a range from 20% of the wheelbase in front of the midpoint of the line segment connecting the front and rear axles to 20% of the wheelbase behind the midpoint, a stable posture can be ensured for the rider of a motorized bicycle traveling at a speed of 20 km / h or less. Effect of the Invention

[0013] According to the present invention, a rider can easily place his / her feet on the ground when stopping a motorized bicycle traveling at a low speed. [Brief description of the drawings]

[0014] [Figure 1] 1 is a side view of a motorized bicycle equipped with a body frame structure according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a side view of a main portion of the vehicle body frame structure according to the embodiment. [Diagram 3] FIG. 2 is a plan view of a main portion of the vehicle body frame structure according to the embodiment. [Figure 4] FIG. 2 is an enlarged front view of a main portion of the vehicle body frame structure according to the embodiment. [Diagram 5] FIG. 2 is an enlarged rear view of a main portion of the vehicle body frame structure according to the embodiment. [Figure 6] Enlarged cross-sectional view taken along line AA in Figure 3. [Figure 7] 5A to 5C are explanatory diagrams illustrating a welded portion between a down tube and a rear stay in the body frame structure of the embodiment. [Figure 8] 6A to 6C are explanatory diagrams illustrating a welded portion between a down tube and a rear stay in a vehicle body frame structure according to a modified example of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] [Vehicle body frame structure and motorized bicycle according to the embodiment] 1 to 6, the vehicle body frame structure of the motorized bicycle 1 includes a head pipe 2, a down tube 3 formed of a single tube and extending obliquely downward from the head pipe 2, a pair of left and right rear stays 4,4 fixed to the rear end of the down tube 3, a bottom bridge 5 that is substantially cylindrical and V-shaped in side view and fixed to the rear end of each rear stay 4 by welding or the like, a pair of left and right cylindrical seat stays 6,6 that are fixed to the upper end of each bottom bridge 5 by welding or the like and extend obliquely upward toward the front, a top bridge 7 that is cylindrical and V-shaped in side view and fixed to the upper end of each seat stay 6 by welding or the like, and a cylindrical seat rail 8 that is fixed to the rear end of the rear-extending portion of each top bridge 7 by welding or the like and extends toward the rear. Each frame that constitutes the vehicle body frame structure of this embodiment is preferably made of, for example, stainless steel, aluminum alloy, aluminum, carbon, steel, or the like.

[0016] The down tube 3 is a cylindrical single frame made up of a downward extension portion 31 extending obliquely downward from the head pipe 2, a curved portion 32 formed at the lower end of the downward extension portion 31, and a horizontal portion 33 extending approximately horizontally rearward from the curved portion 32, and the upper end portion of the downward extension portion 31 is fixed to the head pipe 2 by welding or the like. From the viewpoint of improving manufacturing efficiency, the down tube 3 in the illustrated example is formed by combining a pair of left and right halves 34, 34 and fixing the halves 34, 34 to each other by welding or the like.

[0017] A pair of left and right rear stays 4,4 are fixed to the rear end of the horizontal portion 33 of the down tube 3. In this embodiment, the rear stay 4 is formed in a square pipe shape over its entire length, and has a front tubular portion 41 and a rear tubular portion 43 extending in the front-to-rear direction, and an inclined tubular portion 42 inclined so as to expand outward toward the rear, with the inclined tubular portion 42 formed from the rear end of the front tubular portion 41 via a bent portion, and the rear tubular portion 43 formed from the rear end of the inclined tubular portion 42 via a bent portion. The pair of left and right rear stays 4,4 are provided so as to expand rearward in a Y shape in a plan view, and are fixed by welding to the rear end of the horizontal portion 33 of the down tube 3 (see FIG. 7).

[0018] The square pipe-shaped front tubular portions 41, 41 of the pair of left and right rear stays 4, 4 are formed in a rectangular cross section, and the rear end of the horizontal portion 33 of the down tube 3 is also formed in a rectangular cross section. The front tubular portions 41, 41 of each rear stay are overlapped in the left-right direction, and are welded to each other at a weld seam W1 at the front ends of the contact surfaces of the front tubular portions 41, 41, and in this state are fitted inside the rear end of the horizontal portion 33 of the down tube 33. The front tubular portions 41, 41 of the pair of left and right rear stays 4, 4, which are overlapped and fitted inside the rear end of the down tube 3, are welded to the rear end of the down tube 3, and are welded all around the entire circumference of the rear end of the down tube 3 at a weld seam W2 (see FIG. 7).

[0019] Instead of fixing the rear end of the down tube 3 to the pair of left and right rear stays 4·4 by welding as shown in FIG. 7, the rear end of the down tube 3 may be fixed to the pair of left and right rear stays 4·4 by welding as shown in the modified example of FIG. 8. In the modified example of FIG. 8, the square pipe-shaped front tubular parts 41·41 of the pair of left and right rear stays 4·4 are also formed to have a rectangular cross section, and the rear end of the horizontal part 33 of the down tube 3 is also formed to have a rectangular cross section. The front tubular parts 41·41 of the rear stays are overlapped in the left-right direction, and are welded to each other at the weld part W1 at the front end of the contact surface of the front tubular parts 41·41, and in this state are abutted against the rear end surface of the horizontal part 33 of the down tube 33. The front tubular parts 41·41 of the pair of left and right rear stays 4·4 overlapped and abutted against the rear end surface of the down tube 3 are welded to the rear end of the down tube 3, and are welded all around the entire circumference of the rear end of the down tube 3 at the weld part W3.

[0020] One end of a bottom bridge 5, which is V-shaped in side view and substantially cylindrical, is fixed by welding or the like to the rear end of a rear tubular portion 43 extending substantially horizontally toward the rear of the rear stay 4, and the lower end of a seat stay 6 is fixed by welding or the like to the other end of the bottom bridge 5, so that the rear tubular portions 43 of the left and right rear stays 4 and the seat stays 6 are connected by the bottom bridge 5, which is V-shaped in side view. The straight seat stays 6 extend obliquely upward toward the front. The inclination angle of the seat stays 6 with respect to the horizontal is preferably, for example, 50° to 60°.

[0021] One end of a cylindrical top bridge 7, which is V-shaped in side view, is fixed to the upper end of the seat stay 6 by welding or the like, and a front end of a seat rail 8 is fixed to the other end of the top bridge 7 by welding or the like, so that the left and right seat stays 6 and the seat rails 8 are connected by the top bridge 7, which is V-shaped in side view. In this embodiment, the seat rail 8 is formed in a substantially U-shape in plan view, and one end of the seat rail 8 is fixed to the other end of the left top bridge 7 by welding or the like, and the other end of the seat rail 8 is fixed to the other end of the right top bridge 7 by welding or the like. A seat 17, which is substantially L-shaped in side view, is attached to the upper side of the seat rail 8 so as to be placed thereon.

[0022] The rear tubular portion 43 extending substantially horizontally toward the rear of the rear stays 4 connected via the bottom bridge 5 and top bridge 7, the seat stays 6, and the seat rails 8 form an inverted Z-shaped frame in side view, which is provided to protrude to the left and right. A bridge tube 9 is installed between the left seat stay 6 and the right seat stay 6 near the longitudinal middle of the seat stays 6, and both ends of the bridge tube 9 are fixed to the left seat stay 6 and the right seat stay 6, respectively, by welding or the like.

[0023] Between the horizontal portion 33 of the down tube 3 and the bridge tube 9, a rear tube 10 is provided, which extends obliquely upward toward the rear, and the lower end of the rear tube 10 is fixed to the horizontal portion 33 by welding or the like, and the upper end of the rear tube 10 is fixed to the bridge tube 9 near the midpoint of the bridge tube 9 by welding or the like. In the illustrated example, the bridge tube 9 is provided so as to penetrate the rear tube 10, and the rear tube 10 and the bridge tube 9 are fixed by welding. The inclination angle of the rear tube 10 with respect to the horizontal is preferably, for example, 50° to 60°.

[0024] Furthermore, the position where the bridge tube 9 is provided and the position where the rear tube 10 is fixed to the bridge tube 9 are preferably set at a height of 250 to 300 mm from the lowest end of the down tube 3 and at a height of 150 to 200 mm from the position where the rear tube 10 is fixed to the bridge tube 9 to the top surface of the seat rail 8. Furthermore, by setting the position where the bridge tube 9 is provided and the position where the rear tube 10 is fixed to the bridge tube 9 near the middle part in the longitudinal direction of the seat stay 6, cushioning properties of the seat rail 8 and the seat 17 can be obtained, and the rider 100 can be seated comfortably.

[0025] A cylindrical seat support tube 11 is installed between the horizontal cylinder portions 71, 71 extending approximately horizontally in the front-to-rear direction of the left and right top bridges 7, 7, and both ends of the seat support tube 11 are fixed by welding or the like to the horizontal cylinder portions 71, 71 of the left and right top bridges 7, 7, respectively. In addition, a cylindrical seat support tube 12 is installed between the front and rear cylinder portions 81, 81 extending approximately horizontally in the front-to-rear direction of the seat rails 8 at a position near the midpoint of the front and rear cylinder portions 81, and both ends of the seat support tube 12 are fixed by welding or the like to the left and right front and rear cylinder portions 81, 81, respectively. That is, in this embodiment, two seat support tubes 11, 12 are installed.

[0026] A cylindrical handle post 13 is provided above the head pipe 2 and is fixed to the head pipe 2 by fitting, welding or the like, and a cylindrical operating handle 14 is provided at the upper end of the handle post 13. That is, the operating handle 14 is attached to the head pipe 2 via the handle post 13. An operating unit 15 is provided at the grip portion at the tip of the operating handle 14, with which the rider 100 operates the motorized bicycle 1 to drive, stop, decelerate, accelerate, etc. A front fork 16 is provided below the head pipe 2 and is fixed to the head pipe 2 by fitting, welding or the like, and a front wheel 20 is rotatably supported at the lower end of the front fork 16.

[0027] A rear wheel 21 is rotatably supported at a bent portion of the bottom bridge 5, and a motor device 18 is provided to control and operate the rear wheel 21, such as by driving, stopping, decelerating, and accelerating. The motor device 18 and the operating unit 15 are connected by a connection wire that is routed through the inside of the operating handle 14, the handle post 13, the head pipe 2, the down tube 3, and the rear stay 4 (not shown).

[0028] Foot rest portions 22, 22 that locally protrude to the left and right are attached to the down tube 3 in the range from the bent portion 32 to the front of the rear end of the horizontal portion 33, and in the illustrated example, the foot rest portions 22, 22 that locally protrude to the left and right are attached to the horizontal portion 33 near the bent portion 32. Each foot rest portion 22 is composed of a locking rod 221 that is inserted into a through hole in the down tube 3 and fixed by welding or the like around the periphery of the through hole, an upper foot rest half 222 that is provided above the locking rod 221 and engages with and is fixed to the locking rod 221, a lower foot rest half 223 that is provided below the locking rod 221 and engages with the upper foot rest half 222 and is fixed to the upper foot rest half 222 by bolting or the like, and a foot rest plate 224 that is placed on the upper side of the upper foot rest half 222 and fixed.

[0029] Furthermore, the left and right footrests 22·22 are each positioned within a range from within 20% of the length of the wheelbase H on the front side of the midpoint M to within 20% of the length of the wheelbase H on the rear side of the midpoint M, based on the midpoint M of the line segment connecting the front wheel axle 201 of the front wheel 20 and the rear wheel axle 211 of the rear wheel 21, and are positioned within the footrest placement setting area R in Figure 2.

[0030] According to this embodiment, the down tube 3 is formed from a single frame, and foot rests 22 / 22 are attached to the down tube 3 in a range from the curved portion 32 forward of the rear end of the horizontal portion 33, so that the foot rests 22 protrude locally to the left and right. With the midpoint M of the line segment connecting the front wheel axle 201 and the rear wheel axle 211 as the reference point, the foot rests 22 are positioned within a range from within 20% of the wheelbase H in front of the midpoint M to within a range of 20% of the wheelbase H behind the midpoint M. This allows the rider 100 to easily place his or her feet on either the left or right side of the body or in front of or behind the foot rests 22 / 22, enabling the rider 100 to easily place his or her feet on the ground when the motorized bicycle 1 is stopped.

[0031] Also, the length of the horizontal section 33 that the rider 100 straddles when getting on and off can be set long near or at the minimum ground clearance, allowing even a rider 100 who is short or elderly to easily straddle the horizontal section 33 to get on and off the motorized bicycle 1. In other words, it is possible to improve the ease with which the rider 100 straddles the frame, and to improve the ease of getting on and off the rider 100. Also, the rider 100 can use the horizontal sections 33 in front of and behind the footrests 22-22 as footrests, for example, which improves comfort when driving.

[0032] In addition, by positioning the footrest 22 within a range from 20% of the wheelbase H in front of the midpoint M to 20% of the wheelbase H behind the midpoint M, based on the midpoint M of the line segment connecting the front axle 201 and the rear axle 211, a stable posture can be ensured for the rider 100 of the motorized bicycle 1 when traveling at a low speed of 20 km / h or less.

[0033] In addition, by extending the rear tubular portions 43 of the rear stays 4, the seat stays 6, and the seat rails 8 to the left and right and supporting them in the left-right direction by a bridge tube 9, and supporting the Z-shaped frame of the rear tubular portions 43 of the rear stays 4, the seat stays 6, and the seat rails 8, and the bridge tube 9 by a rear tube 10, it is possible to improve impact resistance and shock absorption against side collisions, thereby improving the safety of the rider 100.

[0034] In addition, by connecting the rear tubular portions 43 of the rear stays 4 and the seat stays 6 with a bottom bridge 5 that is V-shaped in side view, and connecting each of the seat stays 6 and the seat rails 8 with a top bridge 7 that is V-shaped in side view, the Z-shaped frame shape of the rear tubular portions 43 of the rear stays 4, the seat stays 6 and the seat rails 8 can be formed more easily, thereby improving the manufacturing efficiency of the body frame structure.

[0035] In addition, by overlapping the front tubular portions 41 of the rear stays 4, 4 in the left-right direction and welding them to each other, fitting them into the rear end of the down tube 3 and welding them around the entire circumference of the rear end of the down tube 3, it is possible to connect the down tube 3 to the rear stay 4 while maintaining the outline, improving the sense of unity between the down tube 3 and the rear stay 4. In addition, the weld length can be reduced compared to a shape and configuration in which the left and right rear stays are welded all around the down tube one by one with a gap between them, and manufacturing efficiency can be improved while obtaining high rigidity. In addition, the strength of the joint between the rear stay 4 and the down tube 3 can be further increased, and it is possible to more reliably prevent moisture such as rainwater from entering the frame through the joint.

[0036] Furthermore, if the front tubular portions 41, 41 of the rear stays 4, 4 are overlapped in the left-right direction and welded to each other, and then abut against the rear end of the down tube 3, and welded around the entire circumference of the rear end of the down tube 3, the down tube 3 can be joined to the rear stay 4 while maintaining its outline, improving the sense of unity between the down tube 3 and the rear stay 4. Furthermore, the weld length can be reduced compared to a shape and configuration in which the left and right rear stays are welded all around the down tube one by one with a gap between them, thereby improving manufacturing efficiency while maintaining high rigidity.

[0037] [Scope of the invention disclosed herein] The inventions disclosed in this specification include, in addition to the inventions and embodiments listed as inventions, those specified by changing partial contents of these to other contents disclosed in this specification, those specified by adding other contents disclosed in this specification to these contents, or those specified by deleting partial contents of these to the extent that partial effects can be obtained, and specifying them as a higher-level concept. The inventions disclosed in this specification also include the following modified examples and added contents.

[0038] For example, the material of each frame constituting the body frame structure of the present invention may be any suitable material within the scope of the present invention, and for example, carbon or the like may be used. Also, in the above embodiment, the pair of left and right halves 34, 34 are made of metal and fixed to each other by welding or the like to form the down tube 3, but the down tube 3 may be formed by bending a metal tube, for example. Also, the configuration of the footrest portion in the present invention is not limited to the footrest portion 22 in the above embodiment, and may be any suitable material within the scope of the present invention. [Industrial Applicability]

[0039] The present invention can be used as a motorized bicycle that travels at low speeds and as a frame structure thereof. [Explanation of symbols]

[0040] 1...motorcycle 2...head pipe 3...down tube 31...downward extension 32...curved portion 33...horizontal portion 34...half body 4...rear stay 41...front tube portion 42...inclined tube portion 43...rear tube portion 5...bottom bridge 6...seat stay 7...top bridge 71...horizontal tube portion 8...seat rail 81...front and rear tube portions 9...bridge tube 10...rear tube 11, 12...seat support tube 13...handle post 14...operating handle 15...operating portion 16...front fork 17...seat 18...motor device 20...front wheel 201...front wheel axle 21...rear wheel 211...rear wheel axle 22...foot rest portion 221...retaining bar 222...upper foot rest half body 223...lower foot rest half body 224...foot rest plate 100...rider W1, W2, W3... Welding section M... Midpoint of the line segment connecting the front and rear axles H... Wheelbase R... Footrest placement setting area

Claims

1. A body frame structure of a motorized bicycle that travels at a low speed of 20 km / h or less, A head pipe to which an operating handle is attached; a down tube extending obliquely downward from the head pipe, the down tube having a horizontal portion extending rearwardly and substantially horizontally from a bent portion at a lower end of the downward extension, The down tube is formed of a single frame, A footrest portion is attached to the down tube in a range from the bent portion to the front of the rear end of the horizontal portion, the footrest portion protruding locally to the left and right, A vehicle body frame structure characterized in that the footrest is positioned within a range from within 20% of the wheel base on the front side of the midpoint of a line segment connecting the front wheel axle and the rear wheel axle to within a range from within 20% of the wheel base on the rear side of the midpoint, based on the midpoint of the line segment.

2. A pair of left and right rear stays are fixed to rear ends of the horizontal portions so as to expand rearward in a Y-shape in a plan view, A rear tubular portion extending substantially horizontally toward the rear of the rear stay, the seat stay, and the seat rail form an inverted Z-shaped frame in a side view and are provided so as to protrude to the left and right, A bridge tube is installed between the left seat stay and the right seat stay, 2. The vehicle body frame structure according to claim 1, wherein the bridge tube is fixed to an upper end of a rear tube, the rear tube having a lower end fixed to the horizontal portion and extending obliquely upward toward the rear.

3. Each of the rear tubular portions and the seat stays are connected by a bottom bridge that is V-shaped in a side view, 3. The vehicle body frame structure according to claim 2, wherein each of said seat stays and said seat rails is connected by a top bridge that is V-shaped when viewed from the side.

4. a front tubular portion of each of the pair of left and right rear stays is formed into a rectangular shape in cross section, The rear end of the down tube is formed into a rectangular shape in cross section, The front tubular portions of the rear stays are overlapped in the left-right direction and welded to each other, and are fitted into the rear end portion of the down tube, 4. The body frame structure according to claim 2, wherein the rear end of the down tube is welded over the entire circumference to the front tubular portion of the rear stay on which the rear end of the down tube is overlapped.

5. a front tubular portion of each of the pair of left and right rear stays is formed into a rectangular shape in cross section, The rear end of the down tube is formed into a rectangular shape in cross section, The front tubular portions of the rear stays are overlapped in the left-right direction and welded to each other, and are brought into contact with the rear end surface of the down tube, 4. The body frame structure according to claim 2, wherein the rear end of the down tube is welded over the entire circumference to the front tubular portion of the rear stay on which the rear end of the down tube is overlapped.

6. A motorized bicycle that travels at a low speed of 20 km / h or less, A head pipe to which an operating handle is attached; a down tube extending obliquely downward from the head pipe, the down tube having a horizontal portion extending rearwardly and substantially horizontally from a bent portion at a lower end of the downward extension, The down tube is formed of a single frame, A footrest portion is attached to the down tube in a range from the bent portion to the front of the rear end of the horizontal portion, the footrest portion protruding locally to the left and right, The motor-driven bicycle is characterized in that the footrest is disposed within a range from within 20% of the wheel base on the front side of the midpoint of a line segment connecting the front and rear wheel axles to within a range from within 20% of the wheel base on the rear side of the midpoint, based on the midpoint of the line segment.

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