Frame manufacturing method and frame

Abstract

The invention discloses a frame manufacturing method and a frame, relates to the technical field of frame production, and aims to solve the problem that a welding seam at the splicing position of an existing motorcycle frame is obvious. According to the technical scheme, the method is characterized by comprising the following steps that S1, a metal plate is provided as a raw material, and a frame blank is formed through cutting; s2, the frame blank is placed in a stretching die on a hydraulic machine to be subjected to pressure forming, deformation of the frame blank is controlled through a cavity of the stretching die, and a continuous streamline curved surface is formed on a frame body; and S3, laser cutting is carried out on the frame body based on artificial intelligence. The method comprises the following sub-steps that S3.1, actual three-dimensional point cloud data of the surface of the stretched and formed frame body are obtained through an optical scanning system. According to the method, dense welding seams of traditional multi-section splicing are thoroughly eliminated through the integrated streamline forming technology, intelligent prediction and self-adaptive correction are conducted on material springback and thermal deformation in combination with the AI dynamic compensation cutting technology, and precise adaptation of the frame contour and the motor interface is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of frame production, more particularly, it relates to a frame manufacturing method and frame. BACKGROUND

[0002] The current motorcycle frame generally adopts a multi-section stamping piece welding forming process. Due to the discrete design of the stamping die, the frame body needs to be divided into several segments for separate forming and then splicing. This method significantly increases the number of welds, which not only affects the continuity of the appearance, but also causes micro-crack risks in the stress concentration area. Especially for the streamlined curved frame, the traditional stamping is difficult to control the material springback, and after forming, it needs to be repeatedly manually trimmed, which causes low production efficiency and cannot guarantee the contour accuracy. More importantly, the dense welds destroy the integrity of the frame surface, and subsequent polishing and filling processes are needed to cover up the traces, which severely restricts the aesthetic value of the product.

[0003] In terms of environmental protection, the traditional frame surface treatment relies on electroplating or chemical conversion coating, which produces heavy metal wastewater containing chromium, nickel and other heavy metals during the process. The increasingly stringent environmental regulations have formed a rigid constraint on it. On the other hand, in order to adapt to different types of motors, manufacturers must pre-open multiple sets of molds and frequently switch production lines, resulting in high idle rate of equipment and soaring production costs. Although existing laser cutting can achieve hole processing, due to the lack of dynamic compensation mechanism for material forming deformation, step-shaped defects often occur at the cutting edge, which still needs secondary machine repair and cannot meet the precise assembly requirements of modular frames.

[0004] Although some enterprises have tried to introduce automated equipment, existing technological innovations have focused on single links, such as welding robots or fixed program cutting, and have not formed a full-process intelligent closed loop. Especially in the deformation compensation link, it still relies on manual experience to preset the correction amount, and it is difficult to respond to material springback and thermal deformation errors in real time when facing complex streamlined curved surfaces. This fragmented "pseudo-intelligence" leads to fluctuations in the fitting accuracy of key interfaces of the frame, forcing the assembly link to adopt redundant designs such as shims, which deviates from the lightweight trend. How to achieve precise coordination from forming to cutting has become a common technical barrier for high-value frame manufacturing. SUMMARY

[0005] In view of the deficiencies in the prior art, the present application aims to provide a frame manufacturing method and frame, which has the advantages of improving the stability and accuracy of frame laser cutting.

[0006] The above technical purpose of the present application is realized by the following technical scheme: a frame manufacturing method, comprising the following steps: S1: providing a metal plate as a raw material, which is cut to form a frame blank; S2: The frame blank is placed in a stretching die on a hydraulic press and pressed into shape. The deformation of the frame blank is controlled by the cavity of the stretching die, so that the frame body forms a continuous streamlined curved surface. S3: Laser cutting of the main frame based on artificial intelligence, including the following sub-steps: S3.1: Obtain the actual three-dimensional point cloud data of the main body surface of the stretched frame through an optical scanning system; S3.2: Input the actual 3D point cloud data and design model into the AI ​​compensation system, predict the material springback and thermal deformation error based on machine learning algorithms, and generate dynamic cutting path compensation parameters; S3.3: Control the laser cutting head according to the dynamic cutting path compensation parameters, and perform the following operations simultaneously: (a) Cut the frame contour edge along the optimized path; (b) Identify the target motor interface specifications based on the motor model database, and automatically generate and cut compatible mounting holes; S3.4: During the cutting process, the quality of the cut is monitored by a vision sensor. If an abnormal geometric deviation is detected, the AI ​​compensation system is triggered to regenerate the compensation path. S4: The frame sections are connected using pulse welding process, and the weld seams are smoothed after welding. S5: The main body of the frame is treated with a pollution-free surface coating to form an integrated appearance.

[0007] The present invention is further configured such that: in S1, the metal plate is a DC06 steel plate, and is recrystallized and annealed before cutting.

[0008] The present invention is further configured such that, in S2, the cavity of the stretching die adopts a continuous gradient curvature design with a curvature radius ≥150mm, thereby reducing the drag coefficient of the frame.

[0009] The present invention is further configured such that, in S3.1, the optical scanning system is a structured light 3D scanner, and the scanning data is transmitted to the cloud AI compensation system in real time.

[0010] The present invention is further configured such that, in S3.2, the machine learning algorithm is a convolutional neural network (CNN), and the training dataset includes historical springback, material stress-strain curves, and environmental temperature and humidity parameters.

[0011] The present invention is further configured as follows: In S3.3(b): the motor model database is associated with the ERP production management system, and the target motor three-dimensional model data is obtained in real time through the API interface, and the coordinates of the mounting hole position are automatically generated. Before the laser cutting head cuts, the position of the local reinforcing ribs of the frame is dynamically optimized in the AI ​​compensation system based on the motor weight distribution data.

[0012] The present invention is further configured such that, in S3.4, the visual sensor integrates an infrared thermal imaging module, which triggers an adaptive reduction of laser power when a local temperature exceeds a threshold.

[0013] The present invention is further configured such that step S4 specifically includes: S4.1: The 3D vision sensor scans the joint area of ​​the frame segments to generate three-dimensional coordinates of the weld trajectory; S4.2: Input the three-dimensional coordinates of the weld trajectory, material thickness, and streamline curvature data into the welding control system, and generate pulse current waveform parameters based on the reinforcement learning algorithm; S4.3: A variable polarity MIG welding torch protected by argon gas is used to weld along an optimized trajectory; S4.4: During the welding process, the molten pool shape is captured by a high-speed camera module. If a hump weld or undercut defect is detected, the wire feed speed and shielding gas flow rate are adjusted immediately. S4.5: After welding, a five-axis CNC machine tool is used to drive a ball end mill to perform contour milling on the weld. S4.6: Apply localized ultrasonic impact to the smoothed weld area.

[0014] The present invention is further configured such that: the pollution-free surface coating treatment in S5 is a micro-arc oxidation process, the film hardness is ≥800HV, and the treatment solution is a chromium-free electrolyte.

[0015] A vehicle frame, manufactured using a vehicle frame manufacturing method, includes a tailgate and two symmetrically arranged frame bodies, wherein the frame bodies are formed with a streamlined profile by a stretching die; The edges of the main frame are laser-cut to form a clear outline boundary; The two main frame bodies are located on both sides of the tailgate, and a space for accommodating the motor and battery is formed between the main frame bodies and the tailgate.

[0016] In summary, the present invention has the following beneficial effects: 1. This invention completely eliminates the dense welds of traditional multi-segment splicing through integrated streamline forming process, and combines AI dynamic compensation cutting technology to intelligently predict and adaptively correct material springback and thermal deformation, so as to achieve precise matching between the frame contour and the motor interface. 2. The synergistic effect of low-damage pulse welding and environmentally friendly surface treatment not only achieves a seamless and invisible effect on the frame surface, but also eliminates heavy metal pollution at the source; 3. The closed-loop control of the entire process data breaks through the limitations of traditional fragmented automation, enabling the streamlined frame to combine lightweight, high strength and flexible manufacturing compatibility, greatly improving the product's market competitiveness and green manufacturing level. Attached Figure Description

[0017] Figure 1 This is a flowchart of the present invention; Figure 2 This is a flowchart of S3 in this invention; Figure 3 This is a flowchart of S4 in this invention; Figure 4 This is a schematic diagram of the structure in the present invention. Figure 1 ; Figure 5 This is a schematic diagram of the structure in the present invention. Figure 2 .

[0018] In the picture: 1. Main frame; 2. Tailgate. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0020] In the description of this invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "sleeved / connected," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] A method for manufacturing a vehicle frame, such as Figure 1 As shown, it includes the following steps: S1: Provide metal sheet as raw material, which is cut into frame blank, wherein the metal sheet is DC06 steel sheet and recrystallized and annealed before cutting.

[0023] In some embodiments, DC06 ultra-deep drawing steel sheet provides a foundation for chassis manufacturing through its unique metallurgical design. Its ultra-low carbon content reduces the influence of interstitial atoms, while the aluminum-killed steel process immobilizes nitrogen atoms. The addition of trace amounts of Ti and Nb forms nanoscale precipitates, which helps improve the material's plastic strain ratio (r) and gives the billet excellent tensile forming properties. This characteristic enables stable thinning rates in subsequent small-curvature drawing processes, reducing the risk of necking compared to ordinary materials. Simultaneously, its single-phase ferrite structure avoids the martensitic phase transformation in the heat-affected zone of laser cutting, resulting in smaller hardness fluctuations, which is beneficial for subsequent precision machining.

[0024] Pre-cut recrystallization annealing and temper rolling synergistically regulate the microstructure of the material: annealing at an appropriate temperature transforms the distorted grains after cold rolling into equiaxed ferrite, reducing dislocation density; subsequent temper rolling with a certain elongation eliminates the yield plateau, stabilizes the strength, reduces anisotropy, and significantly decreases residual stress. This treatment results in excellent flatness of the billet, more uniform material flow during subsequent stretching and molding, and avoids wrinkling defects.

[0025] S2: The frame blank is placed in a stretching die on a hydraulic press and pressed into shape. The deformation of the frame blank is controlled by the cavity of the stretching die, so that the frame body 1 forms a continuous streamlined curved surface. The cavity of the stretching die adopts a continuous gradient curvature design with a curvature radius ≥150mm to reduce the wind resistance coefficient of the frame. In some embodiments, the continuous gradient curvature design of the stretching die cavity is the core of achieving a high-precision streamlined surface. A smooth transition surface allows the frame blank to undergo controlled plastic flow during pressurization. The continuity of the cavity surface function ensures a uniform distribution of the material flow velocity field in three-dimensional space, effectively suppressing local stress concentrations caused by traditional abrupt curvature dies and keeping the material thinning rate within a safe threshold. The die surface is mirror-polished and coated with a special coating, reducing the coefficient of friction to below 0.08, further ensuring the accuracy of the surface contour.

[0026] This curvature design not only improves aerodynamic performance but also achieves a near-equal strength distribution in the structure. The high curvature region compensates for stiffness loss through in-plane prestress, while the low curvature region makes full use of the material's original strength, thereby improving the overall specific stiffness of the frame.

[0027] To control springback, the mold system integrates multi-physics control strategies, including uniform cavity temperature control, stepped pressure relief during the holding process, and cavity reverse compensation design based on a predictive model. This significantly reduces springback error and enables the dimensional stability of the curved surface to reach a high level.

[0028] S3: Laser cutting of the frame body 1 based on artificial intelligence, including the following sub-steps: likeFigure 2 As shown, S3.1: The actual three-dimensional point cloud data of the surface of the frame body 1 after stretching and forming is obtained through the optical scanning system, and the scanning data is transmitted to the AI ​​compensation system in real time; In some embodiments, the optical scanning system employs a structured light 3D scanner, achieving high-precision scanning through composite coded grating projection technology. The scanning head projects a near-infrared striped grating onto the curved surface of the vehicle frame, and calculates the absolute phase value using a phase resolution algorithm, achieving sub-micron level measurement accuracy. For highly reflective surfaces, adaptive exposure control suppresses specular reflection noise. After preprocessing, the scanned data is transmitted to the AI ​​compensation system via a high-speed communication channel to ensure data integrity and real-time performance.

[0029] S3.2: Input the actual 3D point cloud data and design model into the AI ​​compensation system, predict the material springback and thermal deformation error based on machine learning algorithms, and generate dynamic cutting path compensation parameters; In some embodiments, the AI ​​compensation system employs a convolutional neural network (CNN) to achieve error prediction by deeply fusing material physics constitutive equations with a data-driven model. The network uses a dual-channel input architecture: channel one converts the spatial deviation between the actual point cloud and the design model into a voxelized tensor, while channel two receives feature parameters derived from the material stress-strain curve and environmental parameters. The network structure includes multiple 3D convolutional layers and fully connected layers. The convolutional kernel weight matrix is ​​initialized by the material model to specifically capture material deformation features. The training dataset contains a large amount of historical springback measurement data, and transfer learning is used to improve prediction accuracy, ultimately keeping the prediction error within a small range.

[0030] The CNN output layer generates dynamic path-cutting compensation parameters, and the fully connected layer at the end of the network maps high-order features to a six-dimensional compensation space, including translation and rotation components. To ensure physical plausibility, the compensation parameter generation module embeds geometric constraints, triggering smoothing correction when the predicted rate of curvature exceeds a threshold. Through model optimization, inference time on edge computing units is shortened, meeting real-time requirements.

[0031] S3.3: Control the laser cutting head according to the dynamic cutting path compensation parameters, and perform the following operations simultaneously: (a) Cut the frame profile edge along the optimized path; (b) Identify the target motor interface specifications based on the motor model database, and automatically generate and cut compatible mounting holes; In some embodiments, the laser cutting system achieves high-precision trajectory tracking through a multi-axis robotic arm and galvanometer collaborative system. Compensation parameters are interpolated and converted into cutting head pose commands, driving the system to adjust spatial coordinates. Different laser modes are used for regions with different curvatures to optimize cutting quality. A synchronously integrated infrared thermal imager monitors the temperature field distribution of the cut in real time, dynamically adjusting process parameters to control the heat-affected zone within a small range.

[0032] The motor model database interacts in real time with the production management system. Upon receiving the order number, it extracts the 3D model of the target motor and generates the coordinates of the mounting holes based on geometric analysis. The system simultaneously acquires the motor's weight distribution parameters, drives the AI ​​compensation system to perform local frame reinforcement design, identifies high-stress areas through finite element topology optimization, and generates a stiffener layout scheme based on a prediction algorithm. Finally, the stiffener coordinates are integrated into the laser cutting path.

[0033] S3.4: During the cutting process, the quality of the cut is monitored by a vision sensor. If an abnormality is detected, the AI ​​compensation system is triggered to regenerate the compensation path. In some embodiments, the vision sensor integrates visible light-infrared dual-mode sensing to achieve simultaneous monitoring of the cut geometry and temperature field. Geometric contours are extracted using an edge detection algorithm to identify various deviations; the temperature field is reconstructed using a thermal imaging channel to calculate the temperature gradient. The dual-channel data, after registration, is input into an anomaly diagnosis model, which makes judgments based on the type of deviation and thermal distribution. When an anomaly is triggered, the system performs a multi-level response: real-time adjustment of laser parameters, regeneration of the compensation path, and updating of the AI ​​model to ensure the stability of the cutting quality.

[0034] like Figure 1 and Figure 3 As shown, S4: The frame segments are connected using pulse welding process, and the weld seam is smoothed after welding. Step S4 specifically includes: S4.1: The 3D vision sensor scans the joint area of ​​the frame segments to generate three-dimensional coordinates of the weld trajectory; S4.2: Input the three-dimensional coordinates of the weld trajectory, material thickness, and streamline curvature data into the welding control system, and generate pulse current waveform parameters based on the reinforcement learning algorithm; S4.3: A variable polarity MIG welding torch protected by argon gas is used to weld along an optimized trajectory; S4.4: During the welding process, the molten pool shape is captured by a high-speed camera module. If a hump weld or undercut defect is detected, the wire feed speed and shielding gas flow rate are adjusted immediately. S4.5: After welding, a five-axis CNC machine tool is used to drive a ball end mill to perform contour milling on the weld. S4.6: Apply localized ultrasonic impact to the smoothed weld area.

[0035] In some embodiments, welding parameters are determined through optimization algorithms, with different pulse parameters used for different curvature regions. During welding, a high-speed camera module monitors the molten pool status in real time. When defect features are detected, the closed-loop control system quickly adjusts the wire feed speed and shielding gas flow rate. After welding, a CNC machine tool is used to perform contour milling of the weld seam, keeping the height difference between the milled surface and the base material within a small range. Subsequently, localized ultrasonic impact is applied to the weld area to generate residual compressive stress on the surface, while simultaneously increasing hardness and significantly improving the weld fatigue life.

[0036] S5: Apply a pollution-free surface coating to the frame body 1 to form an integrated appearance. The pollution-free surface coating process is a micro-arc oxidation process with a film hardness of ≥800HV and the treatment solution is a chromium-free electrolyte.

[0037] In some embodiments, the micro-arc oxidation process achieves ceramicization of the vehicle frame surface through high-voltage pulse discharge in an environmentally friendly chromium-free electrolyte. The electrolyte employs a special formulation, forming nanoparticles that are dispersed throughout the ceramic layer during the discharge process. This process allows the film to grow at a specific rate, forming a gradient composite ceramic layer with low surface micropore density. The high hardness of the film stems from its multi-layered nano-reinforcement architecture, while environmental friendliness is achieved through a multi-closed-loop system. The final coating exhibits excellent corrosion resistance and a beautiful, integrated appearance.

[0038] A type of frame, such as Figure 4-5 As shown, it is made using a chassis manufacturing method, including a tail plate 2 and two symmetrical chassis bodies 1. The chassis bodies 1 have a streamlined profile formed by a stretching mold. The edges of the main frame 1 are laser-cut to form a clear outline boundary; The two frame bodies 1 are located on both sides of the tail plate 2, and a space for accommodating the motor and battery is formed between the frame bodies 1 and the tail plate 2.

[0039] In some embodiments, the frame body 1 is integrally formed by a stretching die, and its streamlined profile is the result of optimization of aerodynamics and structural mechanics. Material grains undergo directional slippage along the curvature gradient of the die, resulting in different mechanical properties in different curvature regions. This design significantly reduces the drag coefficient of the frame body 1 while achieving a uniform strength topology. Laser-cut edges achieve high precision, ensuring a high degree of overlap between the aerodynamic shape and the design model, while eliminating stress concentration sources and improving fatigue life.

[0040] The edges of the frame body 1 are laser-cut to form high-quality geometric boundaries, ensuring macroscopic symmetry and stabilizing assembly gaps. Microscopically, a hardened zone is formed to effectively resist assembly wear. Mounting hole positions are generated in real-time by calling a database and performing geometric analysis based on the target motor model to locate mounting points in low-stress areas. When equipped with a high-performance motor, the system simultaneously generates reinforcing rib structures during the cutting stage to balance power load and lightweight requirements.

[0041] The symmetrical frame body 1 and rear panel 2 form a rational spatial layout with an aerodynamic airfoil-like cross-section, exhibiting excellent aerodynamic and heat dissipation characteristics. When equipped with a battery pack, it boasts high space utilization and excellent thermal management performance. The connection between the frame body 1 and rear panel 2 employs advanced welding and reinforcement processes to ensure the reliability of the spatial structure under high vibration conditions.

[0042] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for manufacturing a vehicle frame, characterized in that, Includes the following steps: S1: Provide metal sheets as raw materials, which are cut into frame blanks; S2: The frame blank is placed in a stretching die on a hydraulic press and pressed into shape. The deformation of the frame blank is controlled by the cavity of the stretching die, so that the frame body forms a continuous streamlined curved surface. S3: Laser cutting of the main frame based on artificial intelligence, including the following sub-steps: S3.1: Obtain the actual three-dimensional point cloud data of the main body surface of the stretched frame through an optical scanning system; S3.2: Input the actual 3D point cloud data and design model into the AI ​​compensation system, predict the material springback and thermal deformation error based on machine learning algorithms, and generate dynamic cutting path compensation parameters; S3.3: Control the laser cutting head according to the dynamic cutting path compensation parameters, and perform the following operations simultaneously: (a) Cut the frame contour edge along the optimized path; (b) Identify the target motor interface specifications based on the motor model database, and automatically generate and cut compatible mounting holes; S3.4: During the cutting process, the quality of the cut is monitored by a vision sensor. If an abnormal geometric deviation is detected, the AI ​​compensation system is triggered to regenerate the compensation path. S4: The frame sections are connected using pulse welding process, and the weld seams are smoothed after welding. S5: The main body of the frame is treated with a pollution-free surface coating to form an integrated appearance.

2. The method for manufacturing a vehicle frame according to claim 1, characterized in that: In S1, the metal sheet is a DC06 steel sheet, and it undergoes recrystallization annealing before cutting.

3. The method for manufacturing a vehicle frame according to claim 1, characterized in that: In S2, the cavity of the stretching die adopts a continuous gradient curvature design with a curvature radius ≥150mm, which reduces the drag coefficient of the frame.

4. The method for manufacturing a vehicle frame according to claim 1, characterized in that: In S3.1, the optical scanning system is a structured light 3D scanner, and the scanning data is transmitted to the cloud AI compensation system in real time.

5. A method for manufacturing a vehicle frame according to claim 1, characterized in that: In S3.2, the machine learning algorithm is a convolutional neural network (CNN), and the training dataset includes historical springback, material stress-strain curves, and environmental temperature and humidity parameters.

6. A method for manufacturing a vehicle frame according to claim 1, characterized in that: In S3.3(b): The motor model database is associated with the ERP production management system. The target motor 3D model data is obtained in real time through the API interface, and the coordinates of the mounting hole positions are automatically generated. Before the laser cutting head cuts, the position of the local reinforcing ribs of the frame is dynamically optimized in the AI ​​compensation system based on the motor weight distribution data.

7. A method for manufacturing a vehicle frame according to claim 1, characterized in that: In S3.4: The visual sensor integrates an infrared thermal imaging module, which triggers an adaptive reduction in laser power when a local temperature exceeds a threshold.

8. A method for manufacturing a vehicle frame according to claim 1, characterized in that: Step S4 specifically includes: S4.1: The 3D vision sensor scans the joint area of ​​the frame segments to generate three-dimensional coordinates of the weld trajectory; S4.2: Input the three-dimensional coordinates of the weld trajectory, material thickness, and streamline curvature data into the welding control system, and generate pulse current waveform parameters based on the reinforcement learning algorithm; S4.3: A variable polarity MIG welding torch protected by argon gas is used to weld along an optimized trajectory; S4.4: During the welding process, the molten pool shape is captured by a high-speed camera module. If a hump weld or undercut defect is detected, the wire feed speed and shielding gas flow rate are adjusted immediately. S4.5: After welding, a five-axis CNC machine tool is used to drive a ball end mill to perform contour milling on the weld. S4.6: Apply localized ultrasonic impact to the smoothed weld area.

9. A method for manufacturing a vehicle frame according to claim 1, characterized in that: The pollution-free surface coating treatment in S5 is a micro-arc oxidation process with a film hardness ≥800HV and a chromium-free electrolyte.

10. A vehicle frame manufactured using the vehicle frame manufacturing method as described in claims 1-9, comprising a tailgate and two symmetrically arranged frame bodies, wherein the frame bodies are formed with a streamlined profile by a stretching die; The edges of the main frame are laser-cut to form a clear outline boundary; The two main frame bodies are located on both sides of the tailgate, and a space for accommodating the motor and battery is formed between the main frame bodies and the tailgate.

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