A commercial vehicle frame multi-working condition optimization method based on use scenarios

Abstract

The application provides a commercial vehicle frame multi-working condition optimization method based on a use scene, belongs to the technical field of vehicle design, and comprises the following steps: obtaining frame development requirements, selecting use working conditions for overall and local optimization of the frame, and determining use scene factors; calculating the section performance of longitudinal beams, optimizing and determining the frame longitudinal beam structure in combination with the use scene; building overall and local frame topology models based on the determined frame longitudinal beam structure, determining frame cross beam information, performing frame topology optimization, and forming a frame preliminary design scheme; performing sensitive analysis on the structure size and position parameters of each position of the frame based on the frame preliminary design scheme, selecting optimization parameters and determining optimal values; checking the performance of the frame, locally adjusting the frame topology model, and determining a final frame design scheme. The application can accurately simulate the frame structure, guide the frame design, and realize frame lightweighting and performance optimization.

Description

Technical Field

[0001] This invention belongs to the field of vehicle design technology, specifically relating to a multi-condition optimization method for commercial vehicle chassis based on usage scenarios. Background Technology

[0002] With the development of the automotive industry and simulation technology, simulation optimization methods have been integrated into the entire process of automotive product development and use, encompassing concept design, product iteration, and product optimization. Taking chassis development as an example, in the vehicle product concept design stage, development requirements can be quantified first, and the design parameters of the chassis structure can be adjusted to find the optimal path to meet these requirements. In the vehicle product iteration and optimization stage, simulation optimization can be used to determine a more detailed chassis structure, such as the length, width, and height of each substructure, as well as the connection relationships between structural components. This allows for lightweighting, modularization, performance optimization, and high reliability and durability of the chassis, thereby saving on chassis development, use, and maintenance costs.

[0003] Current simulation optimization analysis based on vehicle frame mostly focuses on optimizing local structures of the frame, usually only considering the improvement of frame stiffness and frequency values, ignoring the working conditions corresponding to the vehicle frame's usage scenarios, resulting in inaccurate simulation results for the frame.

[0004] This is a shortcoming of the existing technology. Therefore, it is very necessary to provide a multi-condition optimization method for commercial vehicle frames based on usage scenarios to address the above-mentioned defects in the existing technology. Summary of the Invention

[0005] The existing simulation optimization analysis based on vehicle frame in the above-mentioned technologies mostly optimizes the local structure of the vehicle frame, usually only considering the improvement of the frame stiffness and frequency value, ignoring the working conditions corresponding to the vehicle frame's usage scenarios, resulting in inaccurate simulation results. This invention provides a multi-condition optimization method for commercial vehicle frames based on usage scenarios to solve the above-mentioned technical problems.

[0006] This invention provides a multi-condition optimization method for commercial vehicle chassis based on usage scenarios, comprising the following steps: S1. Obtain the chassis development requirements, select operating conditions for overall and partial chassis optimization, and determine usage scenario factors; S2. Calculate the performance of the longitudinal beam section, and optimize and determine the longitudinal beam structure of the frame based on the usage scenario; S3. Based on the determined longitudinal beam structure of the frame, build the overall and local frame topology models, determine the crossbeam information of the frame based on the torque performance, perform frame topology optimization based on the operating conditions, and form a preliminary frame design scheme. S4. Based on the preliminary design of the chassis, sensitivity analysis is performed on the structural dimensions and positional parameters at various locations of the chassis, optimization parameters are selected, and the optimal values ​​of the optimization parameters are determined. S5. Verify the performance of each component of the chassis, make local adjustments to the chassis topology model, and determine the final chassis design scheme.

[0007] Furthermore, the specific steps of step S1 are as follows: S11. Obtain the chassis development requirements and analyze the impact of each substructure on the chassis performance during vehicle use; S12. Select strength conditions, stiffness conditions, and modal analysis as operating conditions for overall and local optimization of the vehicle frame; S13. Determine the vehicle wheelbase, load capacity, materials, and road conditions as usage scenario factors for overall and local optimization of the chassis.

[0008] Furthermore, the specific steps of step S2 are as follows: S21. Obtain the designed longitudinal beam structure of the vehicle frame, calculate the maximum bending moment and torque that the longitudinal beam can withstand based on the section modulus and material parameters, and determine the optimal longitudinal beam section performance; S22. Optimize the longitudinal beam structure of the frame based on the optimal longitudinal beam section performance, and determine the longitudinal beam structure of the frame.

[0009] Furthermore, the specific steps of step S21 are as follows: S211. Obtain the designed longitudinal beam structure of the vehicle frame; S212. Determine if a finite element method exists; If so, proceed to step S214; If not, proceed to step S213; S213. Calculate the maximum vertical and lateral bending moment and the maximum torque that the longitudinal beam can withstand using the maximum torque and bending moment formulas, and proceed to step S215. S214. Use finite element processing software to divide the longitudinal beam section network, calculate the section modulus of bending and torsion resistance, calculate the maximum bending moment and torque that the longitudinal beam can withstand, and proceed to step S215. S215. Compare the calculated maximum bending moment and torque that the longitudinal beam can withstand with the design value and empirical value of the longitudinal beam to determine the optimal longitudinal beam section.

[0010] Furthermore, the specific steps of step S3 are as follows: S31. Based on the defined longitudinal beam structure of the vehicle frame, build a topological model of the vehicle frame and determine the topological region; S32. Determine the optimization variables, optimization constraints, and optimization objectives of the chassis topology model. Based on the chassis working conditions, optimize and control the chassis topology model to obtain the initial topology results, determine the number and position of crossbeams, and complete the overall vehicle topology optimization. S33. Determine the effective force transmission path based on the position of the crossbeam, determine the specific structure of the crossbeam and the specific structure of the connecting plate in the local part of the frame, determine the final crossbeam assembly structure, obtain the vehicle frame, and complete the local topology optimization. S34. Integrate the overall vehicle topology optimization results with the local topology optimization results, and combine them with installation constraints and manufacturability to obtain a determined frame beam assembly structure.

[0011] Furthermore, the specific steps of step S32 are as follows: S321. Introduce a suspension system model, a subframe model, and main / subframe connectors into the chassis topology model; S322. Introduce the structures in the vehicle with loads exceeding the threshold into the chassis topology model as mass points; S323. The optimization objectives of the chassis topology model are to minimize the structural flexibility under single-axle bending, inter-axle bending, and combined bending conditions, and to maximize the torsional stiffness and the torsional frequency. S324. The optimization constraint condition for the chassis topology model is that the upper limit of the optimized structural volume fraction does not exceed the threshold. S325. The optimization variable for the chassis topology model is the region where the crossbeam structure is located, which is adjusted in spatial position; S326. Based on the finite element model of the vehicle frame, optimization variables, optimization constraints and optimization objectives in the topology optimization region, material properties are assigned to each structure of the vehicle, connection relationships are established, the initial topology results of the vehicle frame topology model are obtained, the number and position of crossbeams are determined, and the structure of the machinable crossbeam assembly is determined.

[0012] Furthermore, the specific steps of step S33 are as follows: S331. Select the complete chassis model as the first model, and select the chassis body model as the second model; S332. The optimization objective is to minimize the chassis mass; S333. Based on the first model and the second model, the MMO multi-model topology optimization algorithm is used, and the chassis topology model is locally optimized based on the optimization objective.

[0013] Furthermore, the specific steps of step S4 are as follows: S41. The frame crossbeam assembly structure is obtained based on the frame topology optimization, and the thickness of each structural component and the longitudinal position of the crossbeam are selected as parameters; S42. Calculate the sensitivity of the selected parameters to the frame bending stiffness, torsional stiffness, first three modal frequencies and weight, and normalize the sensitivity according to the weight. S43. Select parameters whose sensitivity is higher than the upper threshold and lower than the lower threshold as optimization parameters; S44. With the minimum mass as the optimization objective, and with the bending and torsional stiffness being greater than or equal to the required values, and the first three modal frequencies being greater than or equal to the required values ​​as optimization constraints, the position of the crossbeam is adjusted within a set range. The thickness of each structural component is determined by combining the optimization results and manufacturing requirements, and the optimal values ​​of the optimization parameters are determined to complete the parameter optimization.

[0014] Furthermore, the specific steps of step S5 are as follows: S51. Build a chassis model based on parameter optimization results; S52. Calculate the performance parameters of strength under typical working conditions based on the chassis model and compare them with the target values; If the requirements are met, output the chassis model as the final optimization result, and the process ends. If the requirements are not met, proceed to step S53; S53. Modulate the internal stress of each local part of the structure within a set amplitude until the target value requirement is met.

[0015] Furthermore, in step S53, when the local stress of a certain structure is higher than the threshold, the structure is adjusted by shape optimization to reduce the maximum stress value.

[0016] The beneficial effects of this invention are as follows: The present invention provides a multi-condition optimization method for commercial vehicle frames based on usage scenarios. According to the influence of each substructure on the frame performance during vehicle use, the corresponding usage conditions are selected to optimize the frame from the whole to the parts. It can accurately simulate the frame structure and guide the frame design, determine the frame material distribution and force transmission path, and achieve frame lightweighting and performance optimization while meeting development goals, thereby improving material utilization and saving usage and maintenance costs.

[0017] Furthermore, the design principle of this invention is reliable, the structure is simple, and it has a very wide range of application prospects.

[0018] Therefore, it is evident that the present invention has outstanding substantive features and significant progress compared with the prior art, and the beneficial effects of its implementation are also obvious. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating an embodiment of the commercial vehicle chassis multi-condition optimization method based on usage scenarios of the present invention.

[0021] Figure 2 This is a flowchart illustrating another embodiment of the commercial vehicle chassis multi-condition optimization method based on usage scenarios of the present invention. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0023] Example 1: like Figure 1 As shown, this invention provides a multi-condition optimization method for commercial vehicle chassis based on usage scenarios, including the following steps: S1. Obtain the chassis development requirements, select operating conditions for overall and partial chassis optimization, and determine usage scenario factors; S2. Calculate the performance of the longitudinal beam section, and optimize and determine the longitudinal beam structure of the frame based on the usage scenario; S3. Based on the determined longitudinal beam structure of the frame, build the overall and local frame topology models, determine the crossbeam information of the frame based on the torque performance, perform frame topology optimization based on the operating conditions, and form a preliminary frame design scheme. S4. Based on the preliminary design of the chassis, sensitivity analysis is performed on the structural dimensions and positional parameters at various locations of the chassis, optimization parameters are selected, and the optimal values ​​of the optimization parameters are determined. S5. Verify the performance of each component of the chassis, make local adjustments to the chassis topology model, and determine the final chassis design scheme.

[0024] Example 2: like Figure 2 As shown, this invention provides a multi-condition optimization method for commercial vehicle chassis based on usage scenarios, including the following steps: S1. Obtain the chassis development requirements, select operating conditions for overall and partial chassis optimization, and determine usage scenario factors; the specific steps of step S1 are as follows: S11. Obtain the chassis development requirements and analyze the impact of each substructure on the chassis performance during vehicle use; S12. Select strength conditions, stiffness conditions, and modal analysis as operating conditions for overall and local optimization of the vehicle frame; S13. Determine the vehicle wheelbase, load capacity, materials, and road conditions as usage scenario factors for overall and local optimization of the chassis; S2. Calculate the longitudinal beam section performance, optimize and determine the frame longitudinal beam structure based on the usage scenario; the specific steps of step S2 are as follows: S21. Obtain the designed longitudinal beam structure of the vehicle frame, calculate the maximum bending moment and torque that the longitudinal beam can withstand based on the section modulus and material parameters, and determine the optimal longitudinal beam section performance; the specific steps of step S21 are as follows: S211. Obtain the designed longitudinal beam structure of the vehicle frame; S212. Determine if a finite element method exists; If so, proceed to step S214; If not, proceed to step S213; S213. Calculate the maximum vertical and lateral bending moment and the maximum torque that the longitudinal beam can withstand using the maximum torque and bending moment formulas, and proceed to step S215. S214. Use finite element processing software to divide the longitudinal beam section network, calculate the section modulus of bending and torsion resistance, calculate the maximum bending moment and torque that the longitudinal beam can withstand, and proceed to step S215. S215. Compare the calculated maximum bending moment and torque that the longitudinal beam can withstand with the design value and empirical value of the longitudinal beam to determine the optimal longitudinal beam section; During vehicle use, the longitudinal beams of the chassis primarily bear impacts from cargo, suspension supports, cab, and other attached structures. These impacts cause deformations in the longitudinal beams, mainly vertical bending, with secondary lateral bending and torsion. Since the longitudinal beams are C-shaped or partially reinforced with C-shapes, the maximum bending moment and torque they can withstand can be calculated using theoretical formulas or finite element preprocessing software. These parameters are then compared with required values ​​to determine the optimal longitudinal beam cross-section. The formulas for calculating the maximum vertical and lateral bending moments are as follows:

[0025] The formula for calculating the maximum tolerable torque is:

[0026] in, The maximum bending moment that the longitudinal beam can withstand. The section modulus is the bending section modulus. For the material's yield strength, The maximum torque that the longitudinal beam can withstand. It is the torsional section modulus; Alternatively, finite element preprocessing software can be used to mesh the longitudinal beam section, and the bending and torsional section moduli of the section can be calculated using the built-in module of the finite element processing software. The maximum bending moment and torque that the longitudinal beam can withstand can be further calculated according to the formula. This method can take into account the influence of the longitudinal beam chamfer on the coefficients, and is more convenient and accurate than theoretical calculation. S22. Optimize the frame longitudinal beam structure based on the optimal longitudinal beam section performance to determine the frame longitudinal beam structure; S3. Based on the determined longitudinal beam structure of the chassis, construct the overall and local chassis topology models, determine the crossbeam information of the chassis based on torque performance, perform chassis topology optimization based on operating conditions, and form a preliminary chassis design scheme; the specific steps of step S3 are as follows: S31. Based on the defined longitudinal beam structure of the vehicle frame, build a topological model of the vehicle frame and determine the topological region; S32. Determine the optimization variables, constraints, and objectives of the chassis topology model. Based on the chassis operating conditions, perform optimization control of the chassis topology model to obtain the initial topology results. Determine the number and position of crossbeams to complete the overall vehicle topology optimization. The specific steps of step S32 are as follows: S321. Introduce a suspension system model, a subframe model, and main / subframe connectors into the chassis topology model; S322. Introduce the structures in the vehicle with loads exceeding the threshold into the chassis topology model as mass points; S323. The optimization objectives of the chassis topology model are to minimize the structural flexibility under single-axle bending, inter-axle bending, and combined bending conditions, and to maximize the torsional stiffness and the torsional frequency. S324. The optimization constraint condition for the chassis topology model is that the upper limit of the optimized structural volume fraction does not exceed the threshold. S325. The optimization variable for the chassis topology model is the region where the crossbeam structure is located, which is adjusted in spatial position; S326. Based on the finite element model of the vehicle frame, optimization variables, optimization constraints and optimization objectives in the topology optimization region, material properties are assigned to each structure of the vehicle, connection relationships are established, the initial topology results of the vehicle frame topology model are obtained, the number and position of crossbeams are determined, and the structure of the machinable crossbeam assembly is determined. For example, the topology optimization variable for the whole vehicle is the area where the crossbeam structure can be used to adjust the spatial position. This area is filled with solid elements, and the filled area is connected to the rest of the frame structure by binding relationship. In order to obtain more deterministic optimization results, optimization control is set, including but not limited to upper and lower draft constraints and left and right symmetry constraints. The optimization discrete parameter can be set to 3, the checkerboard control parameter to 1, the optimization constraint condition is the upper limit of volume fraction of 30%, and the optimization objective is to minimize the structural flexibility, maximize the torsional stiffness, and maximize the torsional frequency under single-axis bending and torsion conditions, inter-axle bending and torsion conditions, and comprehensive bending and torsion conditions. Among them, the single-axle bending-torsion condition, inter-axle bending-torsion condition, and combined bending-torsion condition are applied through forced displacement, and the compliance cannot be directly defined through the built-in response. They need to be calculated through custom formulas. The frame compliance calculation formulas for the single-axle bending-torsion condition and the inter-axle bending-torsion condition are as follows:

[0027] in, For the first A concentrated load, For the first Displacement corresponding to the direction of concentrated load application For the first Forced displacement of each tire contact point For the first Forced displacement reaction force at each tire contact point; The formula for calculating the slenderness ratio under combined bending and torsion conditions is as follows:

[0028] in, For the first Normalization coefficients for single-axis bending-torsion or inter-axis bending-torsion conditions. For the first The probability of occurrence of single-axis bending-torsion or inter-axis bending-torsion conditions. For the first Single-axis bending torsion or inter-axis bending torsion flexibility; S33. Determine the effective force transmission path based on the crossbeam position, determine the specific structure of the crossbeam and connecting plate in the local part of the frame, determine the final crossbeam assembly structure, obtain the vehicle frame, and complete the local topology optimization; the specific steps of step S33 are as follows: S331. Select the complete chassis model as the first model, and select the chassis body model as the second model; S332. The optimization objective is to minimize the chassis mass; S333. Based on the first model and the second model, the MMO multi-model topology optimization algorithm is used, and the frame topology model is locally optimized based on the optimization objective; S34. Integrate the whole vehicle topology optimization results with the local topology optimization results, and combine them with installation constraints and manufacturability to obtain a determined frame crossbeam assembly structure; After the overall vehicle topology optimization calculation is completed, the optimization results of the comprehensive bending and torsional conditions should be the main focus, and the optimization results of other conditions should be the supplement. The optimization results should be interpreted in combination with the frame layout requirements, and an initial frame model of the frame should be constructed. In the model, the crossbeam assembly should be selected from the existing structure library according to the stiffness requirements, or the above optimization process should be repeated with the location of a single crossbeam as the topology area until the form of the crossbeam assembly structure that can be processed is determined. To further improve material utilization and reduce overall vehicle weight, the crossbeam assembly is further optimized locally based on the completed initial frame model. To obtain a more deterministic crossbeam assembly structure, the MMO (Multi-Model Optimization) method is selected, where Model 1 is the complete frame model and Model 2 is the frame body model. Considering the working conditions, the optimization objective is to minimize the mass. S4. Based on the preliminary chassis design, sensitivity analysis is performed on the structural dimensions and positional parameters at various locations of the chassis. Optimization parameters are selected, and their optimal values ​​are determined. The specific steps of step S4 are as follows: S41. The frame crossbeam assembly structure is obtained based on the frame topology optimization, and the thickness of each structural component and the longitudinal position of the crossbeam are selected as parameters; S42. Calculate the sensitivity of the selected parameters to the frame bending stiffness, torsional stiffness, first three modal frequencies and weight, and normalize the sensitivity according to the weight. S43. Select parameters whose sensitivity is higher than the upper threshold and lower than the lower threshold as optimization parameters; S44. With the minimum mass as the optimization objective, and with the bending and torsional stiffness being greater than or equal to the required values, and the first three modal frequencies being greater than or equal to the required values ​​as optimization constraints, the position of the crossbeam is adjusted within a set range. The thickness of each structural component is determined in combination with the optimization results and manufacturing requirements. The optimal values ​​of the optimization parameters are determined, and the parameter optimization is completed. S5. Verify the performance of each component of the chassis, make local adjustments to the chassis topology model, and determine the final chassis design scheme; the specific steps of step S5 are as follows: S51. Build a chassis model based on parameter optimization results; S52. Calculate the performance parameters of strength under typical working conditions based on the chassis model and compare them with the target values; If the requirements are met, output the chassis model as the final optimization result, and the process ends. If the requirements are not met, proceed to step S53; S53. Modulate the stress within a set amplitude for each local part of the structure until the target value requirement is met; when the local stress of a certain structure is higher than the threshold, adjust the structure through shape optimization to reduce the maximum stress value.

[0029] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the invention should also be covered within the protection scope of the invention. Therefore, the protection scope of the invention should be determined by the scope of the claims.

Claims

1. A multi-condition optimization method for commercial vehicle chassis based on usage scenarios, characterized in that, Includes the following steps: S1. Obtain the chassis development requirements, select operating conditions for overall and partial chassis optimization, and determine usage scenario factors; S2. Calculate the performance of the longitudinal beam section, and optimize and determine the longitudinal beam structure of the frame based on the usage scenario; S3. Based on the determined longitudinal beam structure of the frame, build the overall and local frame topology models, determine the crossbeam information of the frame based on the torque performance, perform frame topology optimization based on the operating conditions, and form a preliminary frame design scheme. The specific steps of step S3 are as follows: S31. Based on the defined longitudinal beam structure of the vehicle frame, build a topological model of the vehicle frame and determine the topological region; S32. Determine the optimization variables, optimization constraints, and optimization objectives of the chassis topology model. Based on the chassis working conditions, optimize and control the chassis topology model to obtain the initial topology results, determine the number and position of crossbeams, and complete the overall vehicle topology optimization. The specific steps of step S32 are as follows: S321. Introduce a suspension system model, a subframe model, and main / subframe connectors into the chassis topology model; S322. Introduce the structures in the vehicle with loads exceeding a threshold into the chassis topology model as mass points; S323. The optimization objectives of the chassis topology model are to minimize the structural flexibility under single-axis bending, inter-axle bending, and combined bending conditions, and to maximize the torsional stiffness and the torsional frequency. S324. The optimization constraint condition for the chassis topology model is that the upper limit of the optimized structural volume fraction does not exceed the threshold. S325. The optimization variable for the chassis topology model is the region where the crossbeam structure is located, which is adjusted in spatial position; S326. Based on the finite element model of the vehicle frame, optimization variables, optimization constraints and optimization objectives in the topology optimization region, material properties are assigned to each structure of the vehicle, connection relationships are established, the initial topology results of the vehicle frame topology model are obtained, the number and position of crossbeams are determined, and the structure of the machinable crossbeam assembly is determined. S33. Determine the effective force transmission path based on the position of the crossbeam, determine the specific structure of the crossbeam and the specific structure of the connecting plate in the local part of the frame, determine the final crossbeam assembly structure, obtain the vehicle frame, and complete the local topology optimization. The specific steps of step S33 are as follows: S331. Select the complete chassis model as the first model, and select the chassis body model as the second model; S332. The optimization objective is to minimize the chassis mass; S333. Based on the first model and the second model, the MMO multi-model topology optimization algorithm is used, and the frame topology model is locally optimized based on the optimization objective; S34. Integrate the whole vehicle topology optimization results with the local topology optimization results, and combine them with installation constraints and manufacturability to obtain a determined frame crossbeam assembly structure; S4. Based on the preliminary design of the chassis, sensitivity analysis is performed on the structural dimensions and positional parameters at various locations of the chassis, optimization parameters are selected, and the optimal values ​​of the optimization parameters are determined. S5. Verify the performance of each component of the chassis, make local adjustments to the chassis topology model, and determine the final chassis design scheme.

2. The multi-condition optimization method for commercial vehicle chassis based on usage scenarios as described in claim 1, characterized in that, The specific steps of step S1 are as follows: S11. Obtain the chassis development requirements and analyze the impact of each substructure on the chassis performance during vehicle use; S12. Select strength conditions, stiffness conditions, and modal analysis as operating conditions for overall and local optimization of the vehicle frame; S13. Determine the vehicle wheelbase, load capacity, materials, and road conditions as usage scenario factors for overall and local optimization of the chassis.

3. The use-case-based commercial vehicle frame multi-condition optimization method of claim 2, wherein, The specific steps of step S2 are as follows: S21. Obtain the designed longitudinal beam structure of the vehicle frame, calculate the maximum bending moment and torque that the longitudinal beam can withstand based on the section modulus and material parameters, and determine the optimal longitudinal beam section performance; S22. Optimize the longitudinal beam structure of the frame based on the optimal longitudinal beam section performance, and determine the longitudinal beam structure of the frame.

4. The use-case-based commercial vehicle frame multi-condition optimization method of claim 3, wherein, The specific steps of step S21 are as follows: S211. Obtain the designed longitudinal beam structure of the vehicle frame; S212. Determine if a finite element method exists; If so, proceed to step S214; If not, proceed to step S213; S213. Calculate the maximum vertical and lateral bending moment and the maximum torque that the longitudinal beam can withstand using the maximum torque and bending moment formulas, and proceed to step S215. S214. Use finite element processing software to divide the longitudinal beam section network, calculate the section modulus of bending and torsion resistance, calculate the maximum bending moment and torque that the longitudinal beam can withstand, and proceed to step S215. S215. Compare the calculated maximum bending moment and torque that the longitudinal beam can withstand with the design value and empirical value of the longitudinal beam to determine the optimal longitudinal beam section.

5. The multi-condition optimization method for commercial vehicle chassis based on usage scenarios as described in claim 3, characterized in that, The specific steps of step S4 are as follows: S41. The frame crossbeam assembly structure is obtained based on the frame topology optimization, and the thickness of each structural component and the longitudinal position of the crossbeam are selected as parameters; S42. Calculate the sensitivity of the selected parameters to the frame bending stiffness, torsional stiffness, first three modal frequencies and weight, and normalize the sensitivity according to the weight. S43. Select parameters whose sensitivity is higher than the upper threshold and lower than the lower threshold as optimization parameters; S44. With the minimum mass as the optimization objective, and with the bending and torsional stiffness being greater than or equal to the required values, and the first three modal frequencies being greater than or equal to the required values ​​as optimization constraints, the position of the crossbeam is adjusted within a set range. The thickness of each structural component is determined by combining the optimization results and manufacturing requirements, and the optimal values ​​of the optimization parameters are determined to complete the parameter optimization.

6. The use-case-based commercial vehicle frame multi-condition optimization method of claim 5, wherein, The specific steps of step S5 are as follows: S51. Build a chassis model based on parameter optimization results; S52. Calculate the performance parameters of strength under typical working conditions based on the chassis model and compare them with the target values; If the requirements are met, output the chassis model as the final optimization result, and the process ends. If the requirements are not met, proceed to step S53; S53. Modulate the internal stress of each structural part within a set amplitude until the target value requirement is met.

7. The use-case-based commercial vehicle frame multi-condition optimization method of claim 6, wherein, In step S53, when the local stress of a certain structure is higher than the threshold, the structure is adjusted by shape optimization to reduce the maximum stress value.

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