Frame structure and motorized bicycle

Abstract

To enable a rider to easily put his / her foot onto the ground surface when a motorized bicycle stops, and to greatly increase the flexural rigidity of a single frame.SOLUTION: A vehicle body frame structure of a motorized bicycle includes a head tube 2 to which an operation handle 7 is attached, a down tube 3 extending obliquely downward from the head tube 2, a curved part 4 provided in a lower end of the down tube 3, and a rear tube 5 extending obliquely upward from the curved part 4. The down tube 3, the curved part 4, and the rear tube 5 constitutes a single frame formed of a curved pipe of the same metal material. A reinforcement bar 19 laterally protruding from the curved part 4 is passed through a through hole 41 of the curved part 4, and is fixed to a rim of the through hole 41.SELECTED DRAWING: Figure 4

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] Incidentally, for mopeds that are primarily intended to be driven at low speeds, such as certain mopeds that travel at speeds of 20km / h or less, there are many opportunities to stop the vehicle due to the slow speeds at which the vehicle body's behavior becomes unstable. For this reason, it is desirable for the structure to allow the rider to easily place their feet on the ground, but the double frame structure of conventional mopeds is set up so that the frame juts out on both sides, and when the rider stops, they must place their feet on the ground on the outside of the frame that juts out on both sides, making it difficult for the rider to place their feet on the ground.

[0005] A single frame structure is considered for the body frame of a motorized bicycle, as it allows the rider to easily place their feet on the ground. However, a single frame structure has less bending rigidity than a double frame structure, and is more likely to bend or break when the motorized bicycle accelerates or decelerates or when it is hit by a collision. Therefore, a single frame structure with high bending rigidity is required.

[0006] The present invention has been proposed in consideration of the above-mentioned problems, and has as its object to provide a body frame structure and a moped that enable a rider to easily place their feet on the ground when the moped is stopped, while also greatly increasing the bending rigidity of the single frame. [Means for solving the problem]

[0007] The body frame structure of the present invention is a body frame structure for a motor-driven bicycle, comprising a head pipe to which an operating handlebar is attached, a down tube extending diagonally downward from the head pipe, a curved portion provided at the lower end of the down tube, and a rear tube extending diagonally upward from the curved portion, wherein the down tube, the curved portion and the rear tube are a single frame formed from a bent pipe of the same metal material, and a reinforcing bar protruding in the left-right direction from the curved portion is inserted into a through hole in the curved portion and fixed to the periphery of the through hole. According to this, by forming the down tube, the bent portion, and the rear tube from a single frame, foot rests can be provided at positions where the rider can easily place his / her feet on the ground on both the left and right sides of the body, making it possible for the rider to easily place his / her feet on the ground when the motorized bicycle is stopped. Also, by forming the single frame from bent pipes of the same metal material and fixing reinforcing bars protruding in the left and right directions from the bent portion by engaging them with through holes in the bent portion, the bending rigidity of the single frame that constitutes the body frame can be greatly increased.

[0008] The vehicle body frame structure of the present invention is characterized in that the reinforcing bar protruding in the left and right directions from the bent portion is formed as a continuous bar and is provided penetrating through the left and right through holes. This makes it possible to further increase the bending rigidity of the single frame that constitutes the body frame.

[0009] The vehicle body frame structure of the present invention is characterized in that the reinforcing bar is tubular. According to this, by making the reinforcing bar cylindrical, it is possible to increase the bending rigidity of the single frame that constitutes the body frame while reducing the weight of the vehicle.

[0010] The vehicle body frame structure of the present invention is characterized in that a footrest portion is engaged and fixed to the reinforcing bar. The vehicle frame structure of the present invention is a vehicle frame structure for a motor-driven bicycle that travels at a low speed of 20 km / h or less, comprising a head pipe to which an operating handle is attached, a down tube extending diagonally downward from the head pipe, a bent portion provided at the lower end of the down tube, and a rear tube extending diagonally upward from the bent portion, the down tube, the bent portion, and the rear tube, which are all V-shaped in side view, are a single frame formed of a bent pipe of the same metal material, and a reinforcing bar protruding in the left and right directions from the bent portion is formed as a series, is provided to pass through left and right through holes of the bent portion, and is fixed to the periphery of the left and right through holes, and a footrest is engaged and fixed to the reinforcing bar. The vehicle frame structure of the present invention is further characterized in that no reinforcing member is provided above or below the fixed portion between the head pipe and the down tube. According to this, the foot rest portion on which the driver places his / her feet can be easily positioned and fixed by utilizing the reinforcing bar that increases the strength of the body frame.

[0011] The moped of the present invention comprises a head pipe to which an operating handle is attached, a down tube extending diagonally downward from the head pipe, a curved portion provided at the lower end of the down tube, and a rear tube extending diagonally upward from the curved portion, and is characterized in that the down tube, the curved portion and the rear tube are a single frame formed from a bent pipe of the same metal material, and the moped has a body frame structure in which a reinforcing bar protruding in the left-right direction from the curved portion is passed through a through hole in the curved portion and fixed to the periphery of the through hole. According to this, by forming the down tube, the bent portion, and the rear tube from a single frame, foot rests can be provided at positions where the rider can easily place his / her feet on the ground on both the left and right sides of the body, making it possible for the rider to easily place his / her feet on the ground when the motorized bicycle is stopped. Also, by forming the single frame from bent pipes of the same metal material and passing reinforcing bars protruding in the left and right directions from the bent portion through the through holes in the bent portion and fixing them, the bending rigidity of the single frame that constitutes the body frame can be greatly increased.

[0012] The motor-driven bicycle of the present invention is characterized in that the reinforcing bar protruding in the left and right directions from the bent portion is formed as a continuous bar and is provided penetrating through the left and right through-holes. The moped of the present invention is a moped that travels at a low speed of 20 km / h or less, and is characterized in that it comprises a head pipe to which an operating handle is attached, a down tube extending diagonally downward from the head pipe, a bent portion provided at the lower end of the down tube, and a rear tube extending diagonally upward from the bent portion, the down tube, the bent portion, and the rear tube, which are all V-shaped in side view, are a single frame formed of a bent pipe of the same metal material, and a reinforcing bar protruding in the left and right directions from the bent portion is formed as a series, is provided to pass through left and right through holes of the bent portion, and is fixed to the periphery of the left and right through holes, and a footrest is engaged and fixed to the reinforcing bar. The moped of the present invention is further characterized in that it has a body frame structure in which no reinforcing member is provided above or below the fixed portion between the head pipe and the down tube. This makes it possible to further increase the bending rigidity of the single frame that constitutes the body frame. Effect of the Invention

[0013] According to the present invention, it is possible to easily place a rider's feet on the ground when the motorized bicycle is stopped, and it is possible to greatly increase the bending rigidity of the single frame that constitutes the body frame. [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 the vehicle body frame structure according to the embodiment. [Diagram 3] FIG. 2A is a plan view of a vehicle body frame structure according to an embodiment, and FIG. 2B is an enlarged end view of the AA line in FIG. [Figure 4] An enlarged view of the main part of FIG. 3(b). [Diagram 5] FIG. 5 is an enlarged view of a main portion of a vehicle body frame structure according to a modified example, the view corresponding to FIG. 4 . [Figure 6] (a) is a side view of the single frame of analysis example 1, and (b) is an enlarged end view of the BB in (a) of the same figure. [Figure 7] (a) is a side view of the single frame of analysis example 2, and (b) is an enlarged end view of the CC in (a) of the same figure. [Figure 8] (a) is a side view of a single frame of a comparative example, and (b) is an enlarged end view of the double-ended portion of (a) in the same figure. [Figure 9] 13 is a graph showing analysis results showing the relationship between the load applied to the single frame and the displacement difference in analysis example 1, analysis example 2, and comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] [Vehicle body frame structure and motorized bicycle according to the embodiment] A motorized bicycle 1 equipped with a vehicle body frame structure according to an embodiment of the present invention is a motorized bicycle 1 that travels at a low speed, preferably 20 km / h or less, and the vehicle body frame structure of the motorized bicycle 1, as shown in Figures 1 to 3, includes a head pipe 2, a down tube 3 extending obliquely downward from the head pipe 2, a bent portion 4 provided at the lower end of the down tube 3, and a rear tube 5 extending obliquely upward from the bent portion 4, the down tube 3, the bent portion 4, and the rear tube 5 being formed of a substantially cylindrical single frame extending in a straight line in a plan view. The down tube 3, the bent portion 4, and the rear tube 5 in this embodiment are formed of bent pipes made of the same metal material, such as stainless steel, aluminum alloy, or aluminum-carbon-steel.

[0016] The down tube 3, curved portion 4, and rear tube 5, which are made up of a single frame, preferably have the required strength required for the body frame structure of a motorized bicycle 1 traveling at a low speed of 20 km / h, and furthermore, the strength is further increased by penetrating and fixing a reinforcing bar 19, which will be described later, to the curved portion 4. From the viewpoint of ensuring the required strength as a body frame and making it easier for the rider to place his / her feet on the ground when stopped, the left and right widths of the down tube 3 and curved portion 4 are preferably formed to be 350 mm to 450 mm, more preferably 350 mm to 400 mm, and the left and right widths of the rear tube 5 are preferably formed to be 600 mm to 700 mm, more preferably 600 mm to 650 mm.

[0017] A cylindrical handle post 6 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 7 that is generally U-shaped in plan view is provided at the upper end of the handle post 6. That is, the operating handle 7 is attached to the head pipe 2 via the handle post 6. An operating unit 8 that allows a rider 100 to operate the motorized bicycle 1 to drive, stop, decelerate, accelerate, etc. is provided at the grip portion at the tip of the operating handle 7. A front fork 9 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 10 is rotatably supported at the lower end of the front fork 9.

[0018] A cylindrical rear stay 11 is provided on the rear side of the bent portion 4, and the rear stay 11 is fixed to the rear side of the bent portion 4 by welding or the like, and is provided so as to extend rearward substantially horizontally. The upper end of a seat stay 12 extending diagonally downward toward the rear is fixed to a position near the upper side of the rear tube 5 by welding or the like, and the seat stay 12 and the rear stay 11 are arranged in a substantially V-shape in side view. A rear wheel 13 is rotatably supported at the intersection of the rear end of the seat stay 12 and the lower end of the rear stay 11, and a motor device 14 is provided to control and operate the rear wheel 13 by driving, stopping, decelerating, accelerating, etc. The motor device 14 and the operating unit 8 are connected by a connection wire that is wired through the inside of the operating handle 7, the handle post 6, the head pipe 2, the down tube 3, the bent portion 4, and the rear stay 11 (not shown).

[0019] A seat support tube 15 is provided at a position above the fixed portion of the seat stay 12 on the rear tube 5 so as to be substantially horizontal and slightly inclined downward toward the rear. The seat support tube 15 is composed of a left U-shaped pipe material 151 located on the left side in a plan view and a right U-shaped pipe material 152 located on the right side in a plan view, and one end of the left U-shaped pipe material 151 located on the rear side and one end of the right U-shaped pipe material 152 are fixed to the rear tube 5 by welding or the like at the same height. The other end of the left U-shaped pipe material 151 located on the front side and the other end of the right U-shaped pipe material 152 are fitted together to form the seat support tube 15, which is substantially rectangular in a plan view and supports the seat 17 to be placed and fixed.

[0020] The underside of the front end of the seat support tube 15 is supported by a left support stay 161 and a right support stay 162 which are roughly L-shaped in side view. One end of the left support stay 161 arranged on the lower side and one end of the right support stay 162 arranged on the lower side are fixed by welding or the like at the same height to the rear tube 5 at an intermediate position of the rear tube 5 which is lower than the fixing point of the seat stay 12. The other end of the left support stay 161 arranged on the upper side is fixed by welding or the like to the lower side of the left U-shaped pipe material 151, and the other end of the right support stay 162 arranged on the upper side is fixed by welding or the like to the lower side of the right U-shaped pipe material 152.

[0021] In this embodiment, the inclination angle of the rear tube 5 with respect to the horizontal is preferably 40° to 50°, and more preferably 40° to 45°, and the seat support tube 15 is provided at a height of preferably 300 mm to 450 mm, and more preferably 400 mm to 450 mm, from the lowest end of the curved portion 4 of the rear tube 5, and a seat 17 that is approximately L-shaped in side view is placed on the seat support tube 15 installed at this height.

[0022] The curved portion 4 in the body frame structure of the motorized bicycle 1 is positioned within a range from within a range of 20% of the length of the wheel base on the front side of the midpoint M to within a range of 20% of the length of the wheel base on the rear side of the midpoint M, based on the midpoint M of the line segment connecting the front axle 101 of the front wheel 10 and the rear axle 131 of the rear wheel 13, and is positioned within a curved portion position setting region R in Fig. 2. The distance L from the rear end 171 of the seat surface of the seat 17 to the midpoint of the front-to-rear length of a footrest portion 18, which will be described later, is preferably 400mm to 500mm, and more preferably 425mm to 475mm.

[0023] The bent portion 4 is provided with fixed foot rests 18 that locally protrude left and right, and with reinforcing bars 19 that protrude left and right. In this embodiment, the reinforcing bars 19 are cylindrical, and are inserted into and extend through the through holes 41 of the bent portion 4, and are fixed to the bent portion 4 by welding the outer circumferential surface to the peripheries of the left and right through holes 41 with welds 21. The reinforcing bars 19 are fixed so that the left and right protruding lengths from the bent portion 4 are the same and constant (see FIG. 4).

[0024] The foot rest 18 is engaged with and fixed to the reinforcing bar 19, and is attached to the reinforcing bar 19. In this embodiment, the foot rest 18 is composed of an upper foot rest half body 181 and a lower foot rest half body 182. The upper foot rest half body 181 is formed with an engagement protrusion 1811 that protrudes downward like a point, and the lower foot rest half body 182 is formed with an engagement protrusion 1821 that protrudes upward like a point. In addition, a point-like upper engagement portion 191 formed with an engagement hole is formed on the upper side of the reinforcing bar 19, and a point-like lower engagement portion 192 formed with an engagement hole is formed on the lower side of the position of the reinforcing bar 19 corresponding to the upper engagement portion 191.

[0025] The upper footrest half 181 is positioned by engaging the engagement protrusion 1811 with the upper engagement portion 191 of the reinforcing bar 19, and the lower footrest half 182 is positioned by engaging the engagement protrusion 1821 with the lower engagement portion 192 of the reinforcing bar 19, and the upper footrest half 181 and the lower footrest half 182 are arranged to match each other. The upper footrest half 181 and the lower footrest half 182 are then detachably fastened together with bolts 20 to form the footrest portion 18.

[0026] According to this embodiment, by forming the down tube 3, the curved portion 4, and the rear tube 5 as a single frame, foot rests 18 are provided at positions where the rider 100 can easily place his / her feet on the ground on both the left and right sides of the body, making it possible for the rider to easily place his / her feet on the ground when the motorized bicycle 1 is stopped. Also, by forming the single frame from curved pipes of the same metal material and inserting and passing reinforcing bars 19 protruding in the left and right directions from the curved portion 4 into and through the through holes 41 of the curved portion 4 and fixing them therein, it is possible to greatly increase the bending rigidity of the single frame that constitutes the body frame.

[0027] Furthermore, by making the reinforcing bar 19 cylindrical, the bending rigidity of the single frame constituting the body frame can be increased while reducing the vehicle weight. Furthermore, by engaging and fixing the footrest 18 to the reinforcing bar 19, the reinforcing bar 19 can be used to increase the strength of the body frame, thereby making it easy to position and fix the footrest 18 on which the driver 100 places his / her feet.

[0028] [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.

[0029] For example, the motorized bicycle to which the body frame of the present invention is applied is not limited to the motorized bicycle 1 that travels at low speed in the above embodiment, but may be an ordinary motorized bicycle as appropriate. The configuration of the seat support tube and the seat in the present invention is not limited to the seat support tube 15 and the seat 17 in the above embodiment, but may be appropriate within the scope of the present invention, and the configuration of the foot rest portion in the present invention is not limited to the foot rest portion 18 in the above embodiment, but may be appropriate within the scope of the present invention.

[0030] Furthermore, in the present invention, the configuration in which the reinforcing bars protruding in the left-right direction from the bent portion are engaged into the through holes of the bent portion and the reinforcing bars are fixed to the periphery of the through holes is not limited to the configuration in which the series of reinforcing bars 19 in the above embodiment penetrates the left and right through holes 41-41 of the bent portion 4, and may be configured, for example, as in the modified example of Figure 5, in which the inner ends of a pair of reinforcing bars 19a-19a are positioned to engage with the left and right through holes 41a-41a of the bent portion 4, and each reinforcing bar 19 is fixed to the periphery of the corresponding through holes 41a, 41a by a weld 21a.

[0031] [Analysis example and comparative example] Next, we will explain the results of bending rigidity analysis by CAE analysis for a single frame of an analysis example corresponding to a single frame of a down tube 3 having a reinforcing bar 19, a bending portion 4, and a rear tube 5 formed from a bent pipe of the same metal material as in the above embodiment, and a single frame of a comparative example.

[0032] As shown in FIG. 6, the single frame of the analysis example 1 is a substantially cylindrical bent pipe composed of a down tube 3i, a bent portion 4i, and a rear tube 5i corresponding to the down tube 3, the bent portion 4, and the rear tube 5, and is made of A6061-T6 aluminum. The thickness of the down tube 3i, the bent portion 4i, and the rear tube 5i is 1.8 mm, and the inner diameter of the down tube 3i, the bent portion 4i, and the rear tube 5i is approximately 67 mm. At a position slightly above the center of the bent portion 4i in a side view, through holes 41i with a diameter of 35 mm are formed on both the left and right sides, and a series of reinforcing bars 19i with a plate thickness of 1.8 mm and an outer diameter of 35 mm corresponding to the reinforcing bar 19 are provided penetrating the opposing through holes 41i·41i. The outer peripheral surface of the reinforcing bar 19i and the periphery of the through hole 41i are circumferentially welded by a weld portion 21i on the outside of the bent portion 4i. The length of the reinforcing bar 19i from its left end to its right end is 225 mm.

[0033] As shown in FIG. 7, the single frame of the analysis example 2 is a substantially cylindrical bent pipe composed of a down tube 3j, a bent portion 4j, and a rear tube 5j corresponding to the down tube 3, the bent portion 4, and the rear tube 5, and is made of A6061-T6 aluminum. The thickness of the down tube 3j, the bent portion 4j, and the rear tube 5j is 1.8 mm, and the inner diameter of the down tube 3j, the bent portion 4j, and the rear tube 5j is about 67 mm. At a position slightly above the center of the bent portion 4j in a side view, through holes 41j with a diameter of 35 mm are formed on both the left and right sides, and the inner ends of a pair of reinforcing bars 19j with a plate thickness of 1.8 mm and an outer diameter of 35 mm are inserted and arranged in the left and right through holes 41j·41j. The outer peripheral surface of the reinforcing bar 19j and the periphery of the through hole 41j are circumferentially welded by the weld portion 21j on the outside of the bent portion 4j. In the configuration of analysis example 2, the distance from the left end of the left reinforcing bar 19j to the right end of the right reinforcing bar 19j is 225 mm.

[0034] As shown in Fig. 8, the single frame of the comparative example is a substantially cylindrical bent pipe made of A6061-T6 aluminum, which is made up of a down tube 3k, a bent portion 4k, and a rear tube 5k corresponding to the down tube 3, the bent portion 4, and the rear tube 5. The plate thickness of the down tube 3k, the bent portion 4k, and the rear tube 5k is 1.8 mm, and the inner diameter of the down tube 3k, the bent portion 4k, and the rear tube 5k is approximately 67 mm. The bent portion 4k does not have a hole such as the through hole 41i or the through hole 41j, and no reinforcing bar is provided.

[0035] For each of the single frames in analysis example 1, analysis example 2, and comparative example, the rear ends of the rear tubes 5i, 5j, and 5k were fixed completely, and an external force F of -2520N to +2520N (the lower arrow of the external force F in Fig. 6 to Fig. 8 indicates a positive external force, and the upper arrow indicates a negative external force) was applied vertically to the upper surface of each of the down tubes 3i, 3j, and 3k near their front ends as shown in Fig. 6 to Fig. 8, and the vertical displacement of point P was analyzed and calculated using CAE analysis software. The CAE analysis software used was PAM-STAMP (manufactured by ESI Japan, Inc.).

[0036] The vertical displacement of point P in the comparative example is d0, the vertical displacement in analysis example 2 is d1, and the vertical displacement in analysis example 1 is d2. The displacement difference between the comparative example and analysis example 2 is L1=d0-d1, and the displacement difference between the comparative example and analysis example 1 is L2=d0-d2. A graph of the analysis results is shown in Figure 8, with the horizontal axis representing the applied load (N) and the vertical axis representing the displacement difference (mm).

[0037] 9, it can be seen from the displacement differences L1 and L2 that the displacement d1 in analysis example 2 and the displacement d2 in analysis example 1 due to the external force F are smaller than the displacement d0 in the comparative example, and it can be seen that analysis example 2 and analysis example 1 have higher bending rigidity than the comparative example. Furthermore, it can be seen that analysis example 2 in which the reinforcing bar 19i penetrates has a higher bending rigidity than analysis example 1. It can also be seen that the effect of improving bending rigidity is greater when the external force is in the - (minus) direction than in the + (plus) direction in both analysis example 2 in which the reinforcing bar 91j is inserted and analysis example 1 in which the reinforcing bar 91i penetrates, and it is considered that the bending rigidity against the force received when the motorized bicycle runs over a step or the like is higher. [Industrial Applicability]

[0038] The present invention can be used in the body frame structure of a motorized bicycle. [Explanation of symbols]

[0039] 1...motorcycle 2...head pipe 3...down tube 4, 4a...bent portion 41, 41a...through hole 5...rear tube 6...handle post 7...operating handle 8...operating portion 9...front fork 10...front wheel 101...front wheel axle 11...rear stay 12...seat stay 13...rear wheel 131...rear wheel axle 14...motor device 15...seat support tube 151...left U-shaped pipe material 152...right U-shaped pipe material 161...left support stay 162...right support stay 17...seat 171...rear end of seat surface 18...foot rest 181...upper foot rest half 1811...engagement protrusion 182...lower foot rest half 1821...engagement protrusion 19...reinforcing bar 191...upper engagement portion 192...lower engagement portion 20...bolt 21, 21a...welded part 100...driver M...midpoint of line segment connecting front wheel axle and rear wheel axle H...wheelbase R...curved part arrangement setting area L...distance from rear end of seat surface to midpoint of front-rear length of footrest 3i, 3j, 3k...down tube 4i, 4j, 4k...curved part 41i, 41j...through hole 5i, 5j, 5k...rear tube 19i, 19j...reinforcing bar 21i, 21j...welded part

Claims

1. A body frame structure for 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; a bent portion provided at a lower end of the down tube; a rear tube extending obliquely upward from the bent portion, a single frame in which the down tube, the bent portion, and the rear tube, each of which is V-shaped in side view, are made of a bent pipe of the same metal material; A vehicle body frame structure characterized in that a reinforcing bar protruding in the left and right directions from the bent portion is formed as a series, passes through the left and right through holes of the bent portion, and is fixed to the periphery of the left and right through holes, and a footrest portion is engaged and fixed to the reinforcing bar.

2. A body frame structure as described in claim 1, characterized in that no reinforcing members are provided above or below the fixed portion between the head pipe and the down tube.

3. 3. A vehicle body frame structure according to claim 1, wherein the reinforcing bar is tubular.

4. 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; a bent portion provided at a lower end of the down tube; a rear tube extending obliquely upward from the bent portion, a single frame in which the down tube, the bent portion, and the rear tube, each of which is V-shaped in side view, are made of a bent pipe of the same metal material; A motor-driven bicycle is characterized in that it has a body frame structure in which a reinforcing bar protruding in the left and right directions from the bent portion is formed as a series, passes through the left and right through holes of the bent portion, and is fixed to the periphery of the left and right through holes, and a footrest is engaged and fixed to the reinforcing bar.

5. A motor-driven bicycle as described in claim 4, characterized in that it has a body frame structure in which no reinforcing members are provided above or below the fixed portion between the head pipe and the down tube.

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