Lightweight design method for battery pack bracket

Abstract

The invention discloses a lightweight design method for a battery pack bracket, and belongs to the technical field of new energy commercial vehicles. The method comprises the steps of carrying out a battery pack bracket mounting modal test, obtaining modal frequency and vibration mode, establishing a finite element analysis model of a battery pack and a bracket, and adjusting material parameters of the battery pack, so that a simulation modal and the vibration mode are consistent with a test modal. The method comprises the following steps: dividing sub-assembly modules of a battery pack bracket according to structural functions, establishing a topological analysis model of the battery pack and the bracket, carrying out topological optimization calculation on the battery pack and the bracket assembly to obtain a topological optimization analysis result model, carrying out model reconstruction on the basis of sectional material sizes of common specifications in the market to obtain a reconstructed finite element calculation model, and carrying out model optimization calculation on the reconstructed finite element calculation model. And carrying out size optimization analysis on the battery pack and the bracket assembly to finally obtain a lightweight scheme with the optimal shape and thickness. According to the invention, the structural functions of the battery brackets are classified, so that batch assembly is facilitated, the assembly efficiency of the battery pack bracket assembly is improved, and the labor cost of a single component is reduced.

Description

Technical Field

[0001] The invention relates to a lightweight design method for a battery pack bracket, and belongs to the technical field of new energy commercial vehicles. Background Art

[0002] As the demand for battery capacity of new energy commercial vehicles continues to increase, the number and quality of battery pack assemblies are also increasing, which puts forward higher reliability requirements for the battery pack bracket that supports the battery pack, thereby prompting the size and thickness of the battery pack bracket to continue to increase to meet the strength requirements. However, the quality of the battery pack assembly and the bracket continues to rise, which will cause the user's cargo volume to decrease in the standard freight scenario, directly reducing the user's profit margin. The lightweight design of the battery pack bracket can not only reduce the company's costs, but also increase the user's profit margin, which can kill two birds with one stone. At present, the material performance parameters of the battery pack are difficult to obtain, so that the credibility of the simulation model is poor, and the lightweight design area of ​​the battery pack and bracket assembly has no clear scope and boundaries. The reconstructed design after topology optimization and size and thickness optimization is difficult to match the common profile specifications in the market, resulting in unsatisfactory optimization results and repeated iterative verification. The structural specifications after optimization analysis are quite different, which is not conducive to the OEM's procurement and production organization. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a lightweight design method for a battery pack bracket to achieve lightweight battery pack bracket structure, and quickly combine the market mature plate specification scheme, reduce the rounding and re-iteration process of subsequent schemes, and save analysis and optimization time; In order to achieve the above purpose / solve the above technical problems, the present invention is implemented by adopting the following technical solutions:

[0004] A lightweight design method for a battery pack bracket, the method comprising: Perform modal testing on the battery pack and bracket assembly to obtain the measured modal frequency and measured vibration shape of the battery pack and bracket assembly; Establish a finite element analysis model of the battery pack and bracket assembly, and adjust the finite element analysis model until the modal frequency and vibration shape of the calculated battery pack and bracket assembly are consistent with the measured physical structural performance of the battery pack, and obtain the adjusted finite element analysis model; Use the adjusted finite element analysis model to perform performance analysis on the battery pack and bracket assembly, and calculate the basic performance analysis results of the battery pack bracket; Divide the battery pack bracket into assembly areas according to the structural form of the battery pack bracket; According to the basic performance analysis results of the battery pack bracket and the assembly area divided by the battery pack bracket, a topology optimization analysis model is established and the topology results are calculated; Reconstruct the finite element analysis model based on the topological results combined with the size specifications of the market structure; Based on the reconstructed finite element analysis model, the battery pack bracket is divided into assembly areas for size optimization analysis to obtain the optimal parameters of the battery pack bracket thickness.

[0005] Optionally, performing a modal test on the battery pack and bracket assembly to obtain the modal frequency and vibration shape of the battery pack and bracket assembly includes: The installation modal test of the battery pack and bracket assembly in the whole vehicle state is carried out. The battery pack and bracket assembly are stimulated by an exciter, the forced vibration acceleration signal of each measuring point is collected, and the load signal is processed to obtain the modal frequency of the assembly within 100 Hz and the corresponding modal vibration shape.

[0006] Optionally, the finite element analysis model of the battery pack and bracket assembly is established, and the finite element analysis model is adjusted to calculate the modal frequency and vibration shape of the battery pack and bracket assembly so as to be consistent with the measured physical structural performance of the battery pack, to obtain the adjusted finite element analysis model, including: Obtain the outer contour model of the battery pack and establish a simplified solid model of the battery pack and bracket assembly with the same outer contour dimensions; Set parameters for simplified solid models; The elastic modulus E value of the battery pack, the damping coefficient of the battery pack and bracket assembly, the center of mass of the water-cooling unit and the power distribution system, and the moment of inertia of the water-cooling unit and the power distribution system in the simplified solid model are adjusted so that the modal frequency of the battery pack and the bracket assembly in the simplified solid model is controlled within 2% of the measured modal frequency error and the vibration mode is consistent with the measured vibration mode, and the adjusted finite element analysis model is obtained.

[0007] Optionally, the step of setting parameters of the simplified entity model includes: Weighing the battery pack body to obtain the weight of the battery pack body; The mesh size of the simplified solid model is set to 10 mm, the elastic modulus of the hexahedral mesh unit is set to E=800 MPa, the Poisson's ratio NU=0.3 is taken as the initial value, and the density value ρ is adjusted to the weight of the battery pack body.

[0008] Optionally, the adjusted finite element analysis model is used to perform performance analysis on the battery pack and bracket assembly, and basic performance analysis results of the battery pack bracket are calculated, including: Collect basic load data of modal, braking, steering and vertical impact; Based on the adjusted finite element analysis model, the basic performance analysis results of the battery pack bracket are calculated according to the basic load data.

[0009] Optionally, the basic performance analysis results of the battery pack bracket include: the first-order modal frequency of the battery pack and bracket assembly, and the maximum displacement under braking, steering and vertical impact.

[0010] Optionally, dividing the battery pack bracket into assembly areas according to the structural form of the battery pack includes: According to the functions of the various components of the battery pack bracket, the battery pack bracket assembly is divided into a battery pack installation layer, a battery pack bracket front and rear surface layers, a battery pack bracket side surface layer, a battery pack bracket upper and lower surface layers and a cooling system installation layer area.

[0011] Optionally, the topology optimization analysis model is established and the topology results are calculated based on the basic performance analysis results of the battery pack bracket and the assembly area of ​​the battery pack, including: A topological analysis model of the topological design area is established with the battery pack installation layer, the front and rear surface layers of the battery pack bracket, the side layer of the battery pack bracket, the upper and lower surface layers of the battery pack bracket and the cooling system installation layer. Combined with the basic performance analysis results of the battery pack bracket, the attenuation percentage of the first-order modal frequency of the battery pack bracket is <5%, and the maximum displacement increase percentage under braking, steering and vertical impact conditions is <5% as constraints. The first-order modal frequency and the maximum displacement under braking, steering and vertical impact are taken as responses, and the minimum mass is taken as the goal. Topological optimization analysis and calculation are performed to obtain the topological optimization analysis results.

[0012] Optionally, based on the reconstructed finite element analysis model, the battery pack bracket is divided into assembly areas for size optimization analysis to obtain the optimal parameters of the battery pack bracket, including: The vertical beams of the front and rear surface layers and the side layers in the reconstructed finite element model are divided into main vertical support beams and auxiliary vertical support beams, and the battery pack support layer is divided into main battery support beams and auxiliary battery support beams; Based on the constraints that the attenuation percentage of the first-order modal frequency of the battery pack bracket is less than 5% and the increase percentage of the maximum displacement under braking, steering and vertical impact conditions is less than 5%, the first-order modal frequency and the maximum displacement under braking, steering and vertical impact are the responses, and the minimum mass is the goal, the optimal thickness parameters of the main vertical support beam, secondary vertical support beam, main battery support beam and secondary battery support beam are calculated.

[0013] Optionally, the main supporting vertical beams are set as the same component and are assigned the same plate thickness and material properties, the secondary supporting vertical beams are set as the same component and are assigned the same plate thickness and material properties, the main battery support beams are set as the same component and are assigned the same plate thickness and material properties, the secondary battery support beams are set as the same component and are assigned the same plate thickness and material properties, the main cooling support beams are set as the same component and are assigned the same plate thickness and material properties, the secondary cooling support beams are set as the same component and are assigned the same plate thickness and material properties, and the plate thickness variables of each plate are set as discrete variables of thickness specifications commonly used in the market.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (1) The analysis model and test of the battery bracket have been adjusted to achieve higher simulation accuracy; (2) The structural functions of the battery bracket are classified, and the structures of each sub-assembly module are consistent, which is conducive to mass production and assembly, improves the assembly efficiency of the battery pack bracket assembly, and reduces the labor cost of a single component; (3) The main and auxiliary support structures of the bracket are set according to the load conditions of the structure, which can make full use of the load differences of the structure and match components of different structural specifications, which is conducive to achieving better lightweight effects; (4) The common process profile specification factors are fully considered during the simulation optimization process, which reduces the rounding and re-iteration process of subsequent solutions, and the simulation results are more practical; To sum up: the present invention can fully consider the commonly used specifications of the panel market during the analysis process, reduce the rounding process of size and shape, and improve the optimization efficiency; the modular classification analysis and design of the product structure is conducive to mass production assembly, improves the assembly efficiency of the battery pack bracket assembly, and reduces the labor cost of a single component. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a method flow chart of an embodiment of a lightweight design method for a battery pack bracket of the present invention; Figure 2 It is a schematic diagram of a battery pack bracket assembly in a lightweight design method for a battery pack bracket of the present invention; Figure 3 It is a schematic diagram of a battery pack support layer in a lightweight design method for a battery pack bracket of the present invention; Figure 4 It is a schematic diagram of the front and rear surface layers in the lightweight design method of the battery pack bracket of the present invention; Figure 5 It is a schematic diagram of the side surface layer in the lightweight design method of the battery pack bracket of the present invention; Figure 6 It is a schematic diagram of the upper and lower surface layers in the lightweight design method of the battery pack bracket of the present invention; Figure 7 It is a schematic diagram of the support layer in the lightweight design method of the battery pack bracket of the present invention; Figure 8 It is a schematic diagram of the classification of vertical beams in the lightweight design method of the battery pack bracket of the present invention; Fig. 9 It is a schematic diagram of the classification of the battery pack support layer in the lightweight design method of the battery pack bracket of the present invention; Fig.10 It is a schematic diagram of the classification of the cooling system support layer. DETAILED DESCRIPTION

[0016] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0017] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0018] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it 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 it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0019] Embodiment 1, as Figure 1 As shown, the present invention discloses a lightweight design method for a battery pack bracket, the method comprising: Step A: performing a modal test on the battery pack and bracket assembly to obtain the measured modal frequency and measured vibration shape of the battery pack and bracket assembly; Step B, establishing a finite element analysis model of the battery pack and bracket assembly, and adjusting the finite element analysis model until the modal frequency and vibration shape of the calculated battery pack and bracket assembly are consistent with the measured physical structural performance of the battery pack, thereby obtaining an adjusted finite element analysis model; Step C, using the adjusted finite element analysis model to perform performance analysis on the battery pack and bracket assembly, and calculating the basic performance analysis results of the battery pack bracket; Step D, dividing the battery pack bracket into assembly areas according to the structural form of the battery pack bracket; Step E: Based on the basic performance analysis results of the battery pack bracket and the assembly area divided by the battery pack bracket, a topology optimization analysis model is established and the topology results are calculated; Step F, reconstructing the finite element analysis model according to the topological results and the size specifications of the market structure; Step G: Based on the reconstructed finite element analysis model, the battery pack bracket is divided into assembly areas for size optimization analysis to obtain the optimal thickness parameters of the battery pack bracket, and the battery pack and bracket are designed according to the optimal parameters.

[0020] In this embodiment, the specific steps are as follows: With respect to step A, performing a modal test on the battery pack and bracket assembly to obtain the modal frequency and vibration shape of the battery pack and bracket assembly includes: For the installation modal test of the battery pack and bracket assembly in the whole vehicle state, the battery pack and bracket assembly is stimulated by a vibration exciter, the forced vibration acceleration signal of each measuring point is collected, and the load signal is processed to obtain the modal frequency of the assembly within 100 Hz and the corresponding modal vibration shape. A further method is to weigh the battery pack body to obtain the weight of the battery pack body; the installation modal test of the battery pack and bracket assembly in the whole vehicle state is carried out by arranging an acceleration sensor on the outer contour part of the battery pack bracket, using a vibration exciter to excite the battery pack and bracket assembly, collecting the forced vibration acceleration signal of each measuring point, and processing the load signal to obtain the modal frequency of the assembly within 100 Hz and the corresponding modal vibration shape.

[0021] In this embodiment, for step B, specifically: Obtain the outer contour model of the battery pack and establish a simplified solid model of the battery pack and bracket assembly with the same outer contour dimensions; The elastic modulus E value of the battery pack, the damping coefficient of the battery pack and bracket assembly, the center of mass of the water-cooling unit and the power distribution system, and the moment of inertia of the water-cooling unit and the power distribution system in the simplified solid model are adjusted so that the modal frequency of the battery pack and the bracket assembly in the simplified solid model is controlled within 2% of the measured modal frequency error and the vibration mode is consistent with the measured vibration mode, and the adjusted finite element analysis model is obtained.

[0022] In this embodiment, step C is as follows: The adjusted finite element analysis model is used to perform performance analysis on the battery pack and bracket assembly, and the basic performance analysis results of the battery pack bracket are calculated, including: Collect basic load data of modal, braking, steering and vertical impact; Based on the adjusted finite element analysis model, the basic performance analysis results of the battery pack bracket are calculated according to the basic load data.

[0023] Furthermore, the basic performance analysis results of the battery pack bracket include: the first-order modal frequency of the battery pack and bracket assembly, and the maximum displacement under braking, steering and vertical impact.

[0024] In this embodiment, with respect to step D, specifically: according to the basic performance analysis results of the battery pack bracket and the assembly area of ​​the battery pack, a topology optimization analysis model is established and the topology results are calculated, including: A topological analysis model of the topological design area is established with the battery pack installation layer, the front and rear surface layers of the battery pack bracket, the side layer of the battery pack bracket, the upper and lower surface layers of the battery pack bracket and the cooling system installation layer. Combined with the basic performance analysis results of the battery pack bracket, the attenuation percentage of the first-order modal frequency of the battery pack bracket is <5%, and the maximum displacement increase percentage under braking, steering and vertical impact conditions is <5% as constraints. The first-order modal frequency and the maximum displacement under braking, steering and vertical impact are taken as responses, and the minimum mass is taken as the goal. Topological optimization analysis and calculation are performed to obtain the topological optimization analysis results.

[0025] For step G, specifically: based on the reconstructed finite element analysis model, the size optimization analysis is performed according to the assembly area of ​​the battery pack bracket to obtain the optimal parameters of the battery pack bracket, including: The vertical beams of the front and rear surface layers and the side layers in the reconstructed finite element model are divided into main vertical support beams and auxiliary vertical support beams, and the battery pack support layer is divided into main battery support beams and auxiliary battery support beams; Based on the constraints that the attenuation percentage of the first-order modal frequency of the battery pack bracket is less than 5% and the increase percentage of the maximum displacement under braking, steering and vertical impact conditions is less than 5%, the first-order modal frequency and the maximum displacement under braking, steering and vertical impact are the responses, and the minimum mass is the goal, the optimal thickness parameters of the main vertical support beam, secondary vertical support beam, main battery support beam and secondary battery support beam are calculated.

[0026] The main supporting vertical beams are set as the same component, and are given the same plate thickness and material properties. The secondary supporting vertical beams are set as the same component, and are given the same plate thickness and material properties. The main battery support beams are set as the same component, and are given the same plate thickness and material properties. The secondary battery support beams are set as the same component and are given the same plate thickness and material properties. The main cooling support beams are set as the same component, and are given the same plate thickness and material properties. The secondary cooling support beams are set as the same component, and are given the same plate thickness and material properties. The plate thickness variables of each plate are set as discrete variables of commonly used specifications in the market.

[0027] Embodiment 2 provides a method for lightweight design of a battery pack bracket, the method comprising: A. Weigh the battery pack body to obtain the weight of the battery pack body; perform installation modal test on the battery pack and bracket assembly in the whole vehicle state, arrange acceleration sensors on the outer contour parts of the battery pack bracket, use exciters to stimulate the battery pack and bracket assembly, collect forced vibration acceleration signals at each measuring point, and process the load signals to obtain the modal frequency within 100 Hz of the assembly and the corresponding modal vibration shape.

[0028] B. Establish a finite element analysis model of the battery pack and bracket assembly, obtain the outer contour model of the battery pack, and establish a simplified solid model of the battery pack assembly with the same outer contour size. The mesh size is 10 mm, the hexahedral mesh unit is set, and its elastic modulus E=800 MPa and Poisson's ratio NU=0.3 are set as initial values. The density value ρ is adjusted until the weight of the battery pack reaches the actual weight in A. Figure 1 The geometric mid-surface of the plate with uniform plate thickness in the battery pack bracket assembly shown in the figure is extracted and discretized using 5mm two-dimensional shell elements, and the casting structure is discretized using 5mm three-dimensional elements. The elastic modulus, Poisson's ratio, density and other parameters of the material are assigned, the bolts are simplified by combining rigid elements and beam elements, the weld elements are simplified by combining three-dimensional elements + flexible elements, and the cooling system and PDU are simulated by mass points + rigid elements, where the mass of the mass element is the mass of the simplified component, and the initial damping coefficient of the system is set to 0.05; the elastic modulus E value of the battery pack, the damping coefficient of the system, the center of mass and the moment of inertia of the mass element are adjusted, so that the calculated modal frequency of the battery pack and bracket assembly and the measured modal error in A are controlled within 2%, and a high-precision finite element analysis model of the battery pack and bracket is obtained.

[0029] C. Based on the finite element analysis model established in B, basic analysis conditions of modal, braking, steering, and vertical impact are established to evaluate the modal characteristics of the battery pack and bracket assembly and its basic performance under conditions such as emergency braking, steering, and vertical impact of the vehicle. The first-order modal frequency of the battery pack and bracket assembly, and the maximum displacement under braking, steering, and vertical impact are calculated.

[0030] D. According to the functions of the components of the battery pack bracket, the battery pack bracket assembly is divided into battery pack installation layers ( Figure 3 As shown), the front and rear surface layers of the battery pack bracket ( Figure 4 As shown), battery pack bracket side surface layer, etc. ( Figure 5 As shown), the upper and lower surface layers of the battery pack bracket ( Figure 6 As shown), cooling system installation layer ( Figure 7 as shown) in equal parts.

[0031] E. According to the division areas of the subassemblies of the battery pack bracket in D, a topological analysis model is established with the battery pack installation layer, the front and rear surface layers of the battery pack bracket, the side layer of the battery pack bracket, the upper and lower surface layers of the battery pack bracket and the cooling system installation layer as the topological design areas. Combined with the basic performance analysis results in C, with the first-order modal frequency attenuation percentage of the battery pack bracket <5%, the maximum displacement increase percentage under braking, steering and vertical impact conditions <5% as constraints, the modal frequency and displacement as responses, and the minimum mass as the goal, a topological optimization analysis and calculation is performed to obtain the topological optimization analysis results.

[0032] F. According to the result file of the last step of topology optimization iteration in E, the penalty coefficient is set to 0.2 to obtain the topology analysis reference model. Based on this reference model, combined with the common size and thickness specifications of market plates, the model is reconstructed to ensure that each layer of the battery pack installation layer is consistent, and the front and rear surface layers of the battery pack bracket are consistent, the side surface layer structure is consistent, and the upper and lower surface layers are consistent. The reconstructed finite element analysis model is obtained.

[0033] G. Reference Figure 8-Figure 10 , the vertical beams of the front and rear surface layers and the side layers of the finite element model in F are divided into the main vertical support beam and the secondary vertical support beam, the battery pack support layer is divided into the main battery support beam and the secondary battery support beam, the main support vertical beam is set as the same component, and the same plate thickness and material properties are assigned, the secondary support vertical beam is set as the same component, and the same plate thickness and material properties are assigned, the main battery support beam is set as the same component, and the same plate thickness and material properties are assigned, the secondary battery support beam is set as the same component, and the same plate thickness and material properties are assigned, the main cooling support beam is set as the same component, and the same plate thickness and material properties are assigned, the secondary cooling support beam is set as the same component, and the same plate thickness and material properties are assigned, the plate thickness variables of each plate are set as discrete variables of the thickness of the common specifications in the market, the response, constraint and target are set in reference E, and the optimal thickness analysis results of each variable are obtained after calculation. In this way, the lightweight structure is achieved, and the mature plate specification scheme in the market can be quickly combined, the rounding and re-iteration process of the subsequent scheme is reduced, and the analysis and optimization time is saved. The module structure of each sub-assembly of the battery pack bracket is consistent, which is conducive to mass production assembly and improves the assembly efficiency of the battery pack bracket assembly.

[0034] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A lightweight design method for a battery pack bracket, characterized in that: The method comprises: Perform modal testing on the battery pack and bracket assembly to obtain the measured modal frequency and measured vibration shape of the battery pack and bracket assembly; Establish a finite element analysis model of the battery pack and bracket assembly, and adjust the finite element analysis model until the modal frequency and vibration shape of the calculated battery pack and bracket assembly are consistent with the measured physical structure performance of the battery pack, and obtain the adjusted finite element analysis model; Use the adjusted finite element analysis model to perform performance analysis on the battery pack and bracket assembly, and calculate the basic performance analysis results of the battery pack bracket; Divide the battery pack bracket into assembly areas according to the structural form of the battery pack bracket; According to the basic performance analysis results of the battery pack bracket and the assembly area divided by the battery pack bracket, a topology optimization analysis model is established and the topology results are calculated; Reconstruct the finite element analysis model based on the topological results combined with the size specifications of the market structure; Based on the reconstructed finite element analysis model, the battery pack bracket is divided into assembly areas for size optimization analysis to obtain the optimal parameters of the battery pack bracket thickness.

2. The lightweight design method for a battery pack bracket according to claim 1, characterized in that: The finite element analysis model of the battery pack and bracket assembly is established, and the finite element analysis model is adjusted to calculate the modal frequency and vibration shape of the battery pack and bracket assembly to be consistent with the measured physical structure performance of the battery pack, to obtain the adjusted finite element analysis model, including: Obtain the outer contour model of the battery pack and establish a simplified solid model of the battery pack and bracket assembly with the same outer contour dimensions; Set parameters for simplified solid models; The elastic modulus E value of the battery pack, the damping coefficient of the battery pack and bracket assembly, the center of mass of the water-cooling unit and the power distribution system, and the moment of inertia of the water-cooling unit and the power distribution system in the simplified solid model are adjusted so that the modal frequency of the battery pack and the bracket assembly in the simplified solid model is controlled within 2% of the measured modal frequency error and the vibration mode is consistent with the measured vibration mode, and the adjusted finite element analysis model is obtained.

3. The lightweight design method for a battery pack bracket according to claim 2, characterized in that: The step of setting parameters of the simplified entity model includes: Weigh the battery pack to obtain the weight of the battery pack itself; The mesh size of the simplified solid model is set to 10 mm, the elastic modulus of the hexahedral mesh unit is set to E=800 MPa, the Poisson's ratio NU=0.3 is taken as the initial value, and the density value ρ is adjusted to the weight of the battery pack body.

4. The method for lightweight design of a battery pack bracket according to claim 1, characterized in that: The modal test of the battery pack and bracket assembly is performed to obtain the modal frequency and vibration shape of the battery pack and bracket assembly, including: The installation modal test of the battery pack and bracket assembly in the whole vehicle state is carried out. The battery pack and bracket assembly are stimulated by an exciter, the forced vibration acceleration signal of each measuring point is collected, and the load signal is processed to obtain the modal frequency of the assembly within 100 Hz and the corresponding modal vibration shape.

5. The lightweight design method for a battery pack bracket according to claim 1, characterized in that: The adjusted finite element analysis model is used to perform performance analysis on the battery pack and bracket assembly, and the basic performance analysis results of the battery pack bracket are calculated, including: Collect basic load data of modal, braking, steering and vertical impact; Based on the adjusted finite element analysis model, the basic performance analysis results of the battery pack bracket are calculated according to the basic load data.

6. The method for lightweight design of a battery pack bracket according to claim 5, characterized in that: The basic performance analysis results of the battery pack bracket include: the first-order modal frequency of the battery pack and bracket assembly, and the maximum displacement under braking, steering and vertical impact.

7. The method for lightweight design of a battery pack bracket according to claim 5, characterized in that: The method of dividing the battery pack bracket into assembly areas according to the structural form of the battery pack includes: According to the functions of the various components of the battery pack bracket, the battery pack bracket assembly is divided into a battery pack installation layer, a battery pack bracket front and rear surface layers, a battery pack bracket side surface layer, a battery pack bracket upper and lower surface layers and a cooling system installation layer area.

8. The method for lightweight design of a battery pack bracket according to claim 7, characterized in that: According to the basic performance analysis results of the battery pack bracket and the assembly area of ​​the battery pack, a topology optimization analysis model is established and the topology results are calculated, including: A topological analysis model of the topological design area is established with the battery pack installation layer, the front and rear surface layers of the battery pack bracket, the side layer of the battery pack bracket, the upper and lower surface layers of the battery pack bracket and the cooling system installation layer. Combined with the basic performance analysis results of the battery pack bracket, the attenuation percentage of the first-order modal frequency of the battery pack bracket is <5%, and the maximum displacement increase percentage under braking, steering and vertical impact conditions is <5% as constraints. The first-order modal frequency and the maximum displacement under braking, steering and vertical impact are taken as responses, and the minimum mass is taken as the goal. Topological optimization analysis and calculation are performed to obtain the topological optimization analysis results.

9. The method for lightweight design of a battery pack bracket according to claim 8, characterized in that: The reconstructed finite element analysis model divides the battery pack bracket into assembly areas for size optimization analysis to obtain the optimal parameters of the battery pack bracket, including: The vertical beams of the front and rear surface layers and the side layers in the reconstructed finite element model are divided into main vertical support beams and auxiliary vertical support beams, and the battery pack support layer is divided into main battery support beams and auxiliary battery support beams; Based on the constraints that the attenuation percentage of the first-order modal frequency of the battery pack bracket is less than 5% and the increase percentage of the maximum displacement under braking, steering and vertical impact conditions is less than 5%, the first-order modal frequency and the maximum displacement under braking, steering and vertical impact are the responses, and the minimum mass is the goal, the optimal thickness parameters of the main vertical support beam, secondary vertical support beam, main battery support beam and secondary battery support beam are calculated.

10. The method for lightweight design of a battery pack bracket according to claim 9, characterized in that: The method of dividing the vertical beams of the front and rear surface layers and the side layers in the reconstructed finite element model into main vertical support beams and auxiliary vertical support beams, and dividing the battery pack support layer into main battery support beams and auxiliary battery support beams, includes: The main supporting vertical beams are set as the same component, and are given the same plate thickness and material properties. The secondary supporting vertical beams are set as the same component, and are given the same plate thickness and material properties. The main battery support beams are set as the same component, and are given the same plate thickness and material properties. The secondary battery support beams are set as the same component and are given the same plate thickness and material properties. The main cooling support beams are set as the same component, and are given the same plate thickness and material properties. The secondary cooling support beams are set as the same component, and are given the same plate thickness and material properties. The plate thickness variables of each plate are set as discrete variables of commonly used specifications in the market.

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