A lightweight optimization method for a structural frame of a heavy truck battery box

Abstract

The application discloses a lightweight optimization method of a structure frame of a heavy truck battery box, and belongs to the field of structure frame optimization design. It comprises the following steps: step 1, constructing different working condition models of the current structure frame; step 2, obtaining stress distribution nephograms of the structure frame under different working conditions through finite element calculation, determining dangerous positions of the structure frame, and determining the safety of the structure frame; step 3, taking the minimum mass as an optimization target, optimizing conditions to meet material safety requirements, implementing topology optimization, and adopting lightweight materials to reduce the weight of the battery box according to the requirements of lightweight design; and step 4, optimizing the safety of the structure frame. The application can perform lightweight optimization on the existing battery box frame, and reduce the weight of the frame while ensuring the strength of the frame.

Description

Technical Field

[0001] This invention belongs to the field of structural frame optimization design, and more specifically, relates to a lightweight optimization method for the structural frame of a heavy-duty truck battery box. Background Technology

[0002] The core technology module of battery-swapping heavy-duty trucks is the on-board battery swapping system, which includes a base and upper frame, and carries a power battery pack. Currently, the driving range of these trucks is only 200 km, making them unsuitable for long-distance freight transport. Therefore, increasing the driving range has become one of the key issues that must be addressed for battery-swapping heavy-duty trucks.

[0003] Typically, increased driving range is related to battery capacity and density. However, due to the heavy weight of battery-swapping heavy trucks, simply increasing battery capacity and density has limited impact on increasing driving range. Furthermore, increasing battery capacity also increases vehicle weight. Therefore, while achieving breakthroughs in battery technology, further research is needed on vehicle lightweighting to improve vehicle power, braking performance, and fuel economy.

[0004] Electric trucks are generally much heavier than their diesel counterparts. This increased weight is due to the limited energy density of individual batteries; to extend driving range, the number of batteries must be increased, resulting in the current higher weight of electric trucks. The application of lightweight vehicle body technology can improve vehicle performance, free up manufacturing resources, and improve work quality and efficiency. By adopting lightweight technologies, the performance of new energy vehicles can be improved, and costs can be saved.

[0005] Currently, due to the large size of battery packs and the numerous components, new energy heavy-duty trucks generally use rear-mounted battery modules to power the vehicle or replace batteries. In research on lightweight battery packs, structural optimization design is a crucial method. By optimizing the structure of the battery pack, its weight can be reduced, lowering the overall vehicle weight and thus improving the vehicle's power performance.

[0006] Chinese patent application number CN202210716271.1, published on January 3, 2023, discloses a battery box for an electric vehicle comprising an aluminum casting extending between and engaging with the BIW or chassis longitudinal beams of the electric vehicle. The aluminum casting includes a bottom wall, side walls, and a plurality of transverse members. The side walls have a pair of longitudinal beams fixedly attached to the BIW or chassis longitudinal beams of the vehicle. The bottom wall, the side walls, and the plurality of transverse members define a structural housing having a plurality of battery compartments and at least one extrusion zone, and the structural housing is a load-bearing member of the electric vehicle.

[0007] Chinese patent application number CN202211536866.5, published on March 21, 2023, discloses a high-strength, lightweight new energy vehicle battery casing, including a main frame, pull wires, and a sealing layer. The main frame is a cylindrical shape with open ends, formed by multiple frame units. The sealing layer covers one end of the main frame. Several through holes are opened on one side of the frame unit, and wire grooves are provided on the other side of the frame unit. The pull wires include warp and weft threads, both of which pass through at least two frame units and the through holes and wire grooves on the frame units. The warp and weft threads interweave in a mesh at the same end of the main frame. The casing also includes several rigid aerogel blocks, which are arranged along the pull wires and located inside the main frame. The rigid aerogel blocks are in contact with each other, and the rigid aerogel blocks near the frame units abut against the frame units.

[0008] Both of the above solutions optimize the battery pack structure for lightweight vehicle design. However, they only describe the specific structure of the optimized battery pack and do not provide a method for optimizing the existing battery pack frame to achieve the optimal battery pack structure. Furthermore, as can be seen from the attached diagrams, both solutions are primarily designed for new energy vehicles, and their optimized frames are not suitable for heavy-duty trucks requiring battery swapping. Summary of the Invention

[0009] 1. The problem to be solved

[0010] To address the problem that existing technologies lack methods for lightweight structural optimization of battery boxes in heavy-duty trucks with battery swapping capabilities, this invention provides a lightweight optimization method for the structural frame of a heavy-duty truck battery box. This method can optimize the existing battery box frame to reduce its weight while maintaining its strength.

[0011] 2. Technical Solution

[0012] To solve the above problems, the present invention adopts the following technical solution.

[0013] A method for lightweighting and optimizing the structural frame of a heavy-duty truck battery box includes the following steps:

[0014] Step 1: Construct different working condition models for the current structural framework;

[0015] Step 2: Obtain stress distribution cloud maps of the structural frame under different working conditions through finite element calculations, determine the dangerous locations of the structural frame, and determine the safety of the structural frame.

[0016] Step 3: With the goal of minimizing mass, the optimization conditions meet the material safety requirements. Topology optimization is implemented, and lightweight materials are used to reduce the weight of the battery box according to the requirements of lightweight design.

[0017] Step 4: Optimize the security of the structural framework.

[0018] As a further improvement to the technical solution, in step 1, different working conditions include random vibrations in the X, Y, and Z directions.

[0019] As a further improvement to the technical solution, in step 1, the model parts are assembled using actual welded connections, bolted connections, and beam contact relationships.

[0020] As a further improvement to the technical solution, in step 1, the loads acting on the structural frame include: the self-weight of the structural frame, the battery pack assembly, the cooling system, the high-voltage box, and the pressure exerted on the structural frame by the control system.

[0021] As a further improvement to the technical solution, in step 2, the maximum stress of the structural frame is compared with the maximum RMS stress of the material to determine the safety of the structure.

[0022] As a further improvement to the technical solution, in step 3, the objective function is to minimize the frame mass, and the condition is that the maximum stress of the frame under different working conditions satisfies the material properties.

[0023] As a further improvement to the technical solution, step 3 specifically involves: selecting the middle column support structure as the design variable, optimizing the middle column support structure model using solid elements, using random vibration conditions as the optimization benchmark, and using stress as the key constraint condition, to construct the following mathematical model:

[0024] Objective function: ;

[0025] Stress constraint: σmax ≤ σ ≤ σe;

[0026] Design variable: xi L ≤ xi ≤ xi U ;

[0027] in, M This refers to the total weight of the structural frame; ρ The density of the material; n The number of units; v i σmax is the element volume; σe is the maximum Von Mises stress at the nodes during the analysis; σe is the allowable maximum stress; xi is the design variable; xi L The lower limit of the value; xi U This represents the upper limit of the possible values.

[0028] Then, based on the model, the optimizable area of ​​the structural frame and the selection of lightweight materials are determined.

[0029] As a further improvement to the technical solution, in step 3, after determining the optimized mathematical model, the original problem is transformed into an unconstrained problem by having the objective function approach the penalty function, so that each iteration proceeds in the direction of minimizing the objective function.

[0030] As a further improvement to the technical solution, in step 3, the middle column support surface is selected as the area that can be optimized.

[0031] As a further improvement to the technical solution, in step 3, T700 rectangular tube is selected as a lightweight material.

[0032] 3. Beneficial effects

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] (1) The present invention provides a lightweight optimization method for the structural frame of a heavy truck battery box. By analyzing the safety characteristics of the structural frame under different working conditions and based on the stress distribution behavior, structural optimization is implemented. This method can specifically and clearly solve the actual frame hazard problem and compare the safety characteristics before and after optimization to clarify the optimization effect.

[0035] (2) The present invention provides a lightweight optimization method for the structural frame of a heavy truck battery box. Lightweighting is used as the objective function, and combined with structural strength, topology optimization is used to obtain the optimal structure. The model structure is adjusted in combination with practicality.

[0036] (3) The present invention provides a lightweight optimization method for the structural frame of a heavy-duty truck battery box. Attached Figure Description

[0037] Figure 1 This is a structural diagram of the frame of a heavy-duty truck battery box;

[0038] Figure 2 A finite element model of the existing structural framework;

[0039] Figure 3a Stress cloud diagram of an existing structural frame under random vibration X-direction conditions;

[0040] Figure 3b Stress cloud diagram of an existing structural frame under random vibration in the Y direction;

[0041] Figure 3c Stress cloud diagram of an existing structural frame under random vibration Z-axis conditions;

[0042] Figure 4 The result is the topology optimization of the existing structural framework;

[0043] Figure 5 This is a diagram of the intermediate column support structure of the optimized structural frame;

[0044] Figure 6 This is a structural diagram of the stiffeners in the structural frame;

[0045] Figure 7 The finite element model of the optimized structural frame;

[0046] Figure 8a The optimized stress cloud diagram of the structural frame under random vibration X-direction conditions;

[0047] Figure 8b The optimized stress cloud diagram of the structural frame under random vibration in the Y direction;

[0048] Figure 8c The optimized stress cloud diagram of the structural frame under random vibration Z-axis conditions. Detailed Implementation

[0049] Exemplary embodiments of the present invention are described in detail below. While these exemplary embodiments have been described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be implemented and various changes may be made to the invention without departing from its spirit and scope. The more detailed description of embodiments of the invention below is not intended to limit the scope of the claimed invention, but is merely illustrative and does not limit the description of the features and characteristics of the invention, in order to suggest the best mode for carrying out the invention and to enable those skilled in the art to practice it. Therefore, the scope of the invention is defined only by the appended claims.

[0050] A method for lightweighting and optimizing the structural frame of a heavy-duty truck battery box includes the following steps:

[0051] Step 1: Construct different working condition models of the current structural framework

[0052] The structural frame of the heavy-duty truck battery box mainly consists of the vehicle-mounted battery swapping base and the vehicle-mounted battery swapping box.

[0053] Construct a three-dimensional geometric model of the structural framework and establish a finite element model of the structural framework.

[0054] The model's parts are assembled using actual welded connections, bolted connections, and beam contact relationships.

[0055] The loads acting on the structural frame mainly include: the self-weight of the structural frame, the pressure of the battery pack assembly, the cooling system, the high-voltage box, the control system and other equipment on the frame.

[0056] The boundary conditions for the random vibration condition are: constrain all six degrees of freedom of the base fixing hole and implement random vibration in the X, Y, and Z directions.

[0057] Step 2: Determine the safety of the current structural framework

[0058] By using finite element analysis, stress distribution cloud maps of the structural frame under different working conditions are obtained, and the dangerous locations of the structural frame are determined.

[0059] The safety of the structural frame is determined by comparing the maximum stress of the structural frame with the material properties.

[0060] Step 3: Perform topology optimization of the structural framework

[0061] The results from step 2 show that the structural frame's safety in the random vibration analysis fails to meet the standard in which direction. Therefore, while ensuring the frame's lightweight objective, it is also necessary to meet structural strength requirements. The intermediate support column structural surface is selected as the design variable for topology optimization. The intermediate support structural surface model is optimized using solid elements, with random vibration conditions as the baseline and stress as the key constraint. After determining the variables and response constraints, a mathematical model is constructed with the goal of minimizing the frame's total mass:

[0062] Objective function: ;

[0063] Stress constraint: σmax ≤ σ ≤ σe;

[0064] Design variable: xi L ≤ xi ≤ xi U ;

[0065] in, M This refers to the total weight of the structural frame; ρ The density of the material; n The number of units; v i σmax is the element volume; σe is the maximum Von Mises stress at the nodes during the analysis; σe is the allowable maximum stress; xi is the design variable; xi L The lower limit of the value; xi U This represents the upper limit of the possible values.

[0066] After determining the optimal mathematical model, a variable density method is adopted to make the topology design lightweight, thereby making the optimization analysis more accurate. To achieve this goal, the original problem is transformed into an unconstrained problem by having the objective function approach the penalty function, ensuring that each iteration moves in the direction of minimizing the objective function.

[0067] The area of ​​the structure that can be optimized was determined. Considering that fixed-size battery packs and other assemblies need to be installed in the structural frame, and that the methods for connecting specific components are not the same, the middle column support surface was selected as the design optimization space.

[0068] To meet the demands of lightweight design, the use of lightweight materials can significantly reduce the weight of the battery pack. Lightweighting of battery pack materials is an inevitable trend in the electric vehicle industry, as it not only improves vehicle performance and driving range but also reduces environmental impact.

[0069] Step 4: Optimize the safety of the structural framework

[0070] The support structure of the central column support surface design space is obtained by using topology optimization, and the structure is adjusted and optimized according to the actual space conditions and practicality.

[0071] Simulations of different working conditions were established for the optimized structure. Steps 1 and 2 were repeated to compare the safety of the structural frame before and after optimization.

[0072] Example 1

[0073] The battery pack for the 49-ton electric drive heavy truck using a rear battery module is as follows: Figure 1 As shown in Table 1, the range of key dimensions for the onboard battery swapping box is listed. A finite element model of the battery module structure of a 49-ton electric heavy-duty truck with a rear battery module is established, as shown below. Figure 2 As shown.

[0074] Random vibration loads and constant-frequency vibration loads are applied to the structure. The boundary conditions of the frame model are set as follows: all six degrees of freedom of the base fixing holes are constrained. The specific loading sequence is as follows: first, a random vibration load is applied in the z-axis direction, and then the constant-frequency vibration is applied; then, vibration tests are performed on the x-axis and y-axis in the same way (the x-axis direction is the vehicle's travel direction by default).

[0075] Table 1 Dimensions of Vehicle-Mounted Battery Swapping Box

[0076]

[0077] In engineering, a practical method for calculating the lifespan of structures under random vibration is the three-interval method, which assumes that the stress follows a Gaussian distribution. According to this method, the stress is divided into three intervals. The vibration time occurring within the stress intervals -1σ~1σ, -2σ~2σ, and -3σ~3σ accounts for 68.3%, 27.1%, and 4.33% of the total time, respectively. Stresses greater than 3σ occur only in 0.27% of the time, and can be considered not to cause significant damage to the structure. Taking Q235 steel as an example, its tensile strength is 370 MPa. According to this model, the maximum allowable RMS stress of the structural frame is 123 MPa. When the maximum RMS stress value of the structural frame under random vibration load is less than the material's yield strength of 123 MPa, the strength meets the requirements; otherwise, the structural frame strength does not meet the requirements and will fail due to insufficient strength.

[0078] Random vibration loads and constant-frequency vibration loads were applied, with the following loading sequence: first, a random vibration load was applied along the z-axis, followed by constant-frequency vibration; then, vibration tests were performed along the x-axis and y-axis in the same manner (the x-axis direction is assumed to be the vehicle's travel direction). Through finite element simulation of the random vibration of the structural frame, the stress distribution cloud diagrams of the structural frame under random vibration in the X, Y, and Z directions are shown in Figure 3. The maximum equivalent stress under random vibration in the X, Y, and Z directions was obtained to verify the strength of the structural frame. The maximum stress values ​​of the structural frame under random vibration in each direction are shown in Table 2. It can be seen that the maximum stress value under random vibration in the Z-direction is less than 123 MPa, but both the X and Y directions are greater than 123 MPa. Under random vibration in the X and Y directions, the stress values ​​are greater than the required values, therefore, the strength of the structural frame does not meet the requirements.

[0079] Table 2 Stress values ​​of the structural frame under various working conditions in random vibration analysis

[0080]

[0081] Based on the mathematical model proposed in step 3, including the objective function, stress constraints, and design variable constraints.

[0082] (1) The objective function is to minimize the total weight of the structure;

[0083] (2) The stress constraint is that the maximum Von Mises stress value at the node is less than the RMS stress value by 123 MPa;

[0084] (3) The design variable is the support surface of the middle column as the design optimization space to ensure that the structure and holes remain basically unchanged, and the outer boundary of the structure, the size and position of the holes remain relatively stable.

[0085] Given the established connection methods between the structural frame and different components, the external boundary of the structure, the size and position of the holes are kept relatively stable to prevent the optimized structure from having an adverse effect on other components.

[0086] The variable density method is adopted to transform the problem into an unconstrained problem by having the objective function approach the penalty function, thus making the optimization analysis more accurate. The results of the calculated output model are as follows: Figure 4 As shown.

[0087] Based on practicality, the structural frame was readjusted, and the V-shaped bracing of the central column was changed to X-shaped bracing to increase the Y-direction stiffness of the structure. The redesigned structural frame is as follows. Figure 5 As shown.

[0088] Based on the requirements of lightweight design, T700 rectangular tubes are used instead of Q235 rectangular tubes. Table 3 below is a list of T700 material rectangular tubes that replace Q235 material rectangular tubes.

[0089] Table 3 Material Change List

[0090]

[0091] To improve the lifespan of the structural frame, reduce the risk of structural failure, and minimize stress concentration, the local structure of the frame was first optimized. Reinforcing ribs were added to each frame layer to increase the strength and stability of the battery load-bearing surface. Figure 6 As shown.

[0092] Based on the above design content, including the design of structural support columns, lightweight material design, and stiffener support design, a new battery swapping structural frame model was obtained, as follows: Figure 7 As shown.

[0093] The rear battery box structure of the aforementioned 49-ton electric heavy truck was substituted into the finite element model for analysis and calculation. Since the optimized structure uses high-strength steel T700 with a tensile strength limit of 700 MPa, the maximum allowable RMS stress of the optimized structure frame reaches 233 MPa. Finite element simulations of the optimized structure frame under random vibration in the X, Y, and Z directions were performed, and the stress distribution cloud maps of the simulation results are shown in Figure 8.

[0094] After the structural frame underwent lightweight replacement with high-strength steel and local structural optimization, the optimized structural frame was obtained. The maximum stress values ​​of the frame under random vibration in the X, Y, and Z directions are shown in Table 4. The results show that the maximum stress of the frame is less than the maximum allowable RMS stress of 233 MPa, indicating that the strength of the optimized frame fully meets the strength requirements and improves the original frame's failure to meet the requirements for random vibration strength in the X and Y directions.

[0095] Table 4. Stress values ​​of the battery frame under various working conditions after optimization by random vibration analysis.

[0096]

[0097] After lightweight design and local structural optimization, the structural frame achieved the goal of weight reduction. The initial structural weight of the battery upper frame was 534.1 kg, and the optimized structural weight was 340.7 kg, resulting in a weight reduction of 193.4 kg, or 36.2%. Furthermore, the optimized design significantly increased the structural safety factor. The optimization results are shown in Table 5, demonstrating significant improvement in product competitiveness.

[0098] Table 5 Comparison and Analysis of Random Vibration Analysis Results of Optimized Schemes

[0099]

[0100] The examples described herein are merely preferred embodiments of the invention and are not intended to limit the concept and scope of the invention. Any modifications and improvements made by those skilled in the art to the technical solutions of the invention without departing from the design concept of the invention should fall within the protection scope of the invention.

Claims

1. A lightweight optimization method for a structural frame of a heavy truck battery box, characterized by: The method comprises the following steps: Step 1: constructing different working condition models of the current structure framework, the different working conditions including random vibration in X, Y and Z directions; Step 2: obtaining stress distribution nephograms of the structure framework under different working conditions through finite element calculation, determining dangerous positions of the structure framework, comparing the maximum stress of the structure framework with the maximum RMS stress of the material, and determining the safety of the structure framework; Step 3: implementing topology optimization with the minimum mass as an optimization objective and the material safety requirement as an optimization condition, and reducing the weight of the battery box by using lightweight materials according to the requirement of lightweight design; In this step, the objective function is the minimum mass of the framework, and the condition is that the maximum stress of the framework under different working conditions meets the material performance; The specific process is as follows: the middle column support structure surface of the framework is selected as a design variable, the middle column support structure surface model is optimized by using body elements, random vibration conditions are used as benchmark conditions for optimization, and stress is used as a key constraint condition, and the following mathematical model is constructed: Objective function: ; Stress constraint: σmax≤σ≤σe Design variables: xi L ≤ xi ≤ xi U ; wherein, M is the total weight of the structural frame; Then, the optimizable area of the structure framework is determined according to the model, and a lightweight material is selected. is the density of the material; n is the number of units; v i is the unit volume; σmax is the maximum Von Mises stress value of the nodes during the analysis; σe is the allowable maximum stress; xi is the design variable; xi L is the lower limit of the value; xi U is the upper limit of the value; Step 4: optimizing the safety of the structure framework. In the step 1, the parts of the model are combined by using actual welding connections, bolt connections and beam contact relationships.

2. The method of claim 1, wherein: In the step 1, the loads acting on the structure framework include the pressure of the structure framework, the battery pack assembly, the cooling system, the high-voltage box and the control system on the structure framework.

3. The method of claim 1, wherein: In the step 2, the maximum stress of the structure framework is compared with the maximum RMS stress of the material to determine the safety of the structure.

4. The method of claim 1, wherein: In the step 3, after the mathematical model of optimization is determined, the original problem is converted into an unconstrained problem in the form of the objective function approaching the penalty function, so that each step of iteration is performed in the direction of minimizing the objective function. 5.The method of claim 1, wherein: In the step 3, the middle column support surface is selected as the optimizable area.

6. The method according to claim 5, wherein: In the step 3, T700 rectangular tubes are selected as the lightweight material.

7. The method according to claim 6, wherein: ​

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