A method for optimizing a battery pack housing structure

Abstract

The application relates to the technical field of batteries, in particular to a battery pack box structure optimization method, which comprises the following steps: establishing a CAE model of a battery pack box structure; calculating the constraint mode of the battery pack box structure; respectively establishing a super unit model for a battery module and an upper cover; and performing size optimization on the lower box based on the super unit model; the optimization method of the application establishes a super unit model for the battery module and the upper cover, defines the battery module and the upper cover as fixed quantities, improves the optimization rate, shortens the product development cycle, uses the constraint mode as an optimization constraint condition, simplifies complex working conditions, improves the optimization efficiency, and ensures the reliability of the optimization result.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a method for optimizing a battery pack box structure. BACKGROUND

[0002] New energy vehicles mainly using pure electric and hybrid power have a broad application prospect in the modern automobile field due to their low carbon, environmental protection and energy saving. In new energy vehicles, the battery box is the main power source and also provides energy for many electric auxiliary systems. Therefore, the reliability, durability, safety and working efficiency of the battery box are directly related to the power performance of the vehicle. When designing the battery box structure, the extrusion, vibration and impact performance indicators are often used as the main development basis. Among them, the vibration fatigue performance of the battery box is the most stringent performance indicator, and the performance of the modal directly affects the vibration fatigue performance. Therefore, modal optimization is extremely important in the process of battery pack optimization.

[0003] Currently, there are mainly the following methods for modal optimization of battery packs based on CAE tools:

[0004] 1) Experience optimization: according to the modal results of CAE analysis, the structure is optimized by combining the experience of engineers. This method is low in efficiency and cannot guarantee that each scheme can contribute to the optimal solution.

[0005] 2) Optimization based on sensitivity analysis: taking modal and weight as the target, the sensitivity of each component thickness parameter of the box body is analyzed first, the components with high sensitivity are thickened, and the components with low sensitivity are thinned. After several manual trial calculations, a relatively suitable scheme is found. Although this method can accurately find the parts that need to be optimized, it cannot find the optimal solution and is low in efficiency.

[0006] 3) Size optimization: taking the complete battery pack model as the analysis object, taking the thickness of each component as the variable parameter, setting the variable value range, taking the weight and modal as the boundary constraints or targets of optimization, and using CAE tools for optimal solution. This scheme can obtain a local optimal solution, but due to the large size of the model, the optimization efficiency is extremely low, and even cannot meet the engineering development cycle.

[0007] 4) Size optimization of simplified module: in order to improve the optimization efficiency, the model of the module is simplified to a mass point. This method can greatly improve the optimization efficiency. However, the structural stiffness of the module itself has a great influence on the overall modal of the battery pack, resulting in low optimization solution accuracy of the simplified model or even incorrect optimization solution.

[0008] 5) DOE optimization: take the complete battery pack model as the analysis object, take the thickness of each component as the variable parameter, and perform DOE test analysis based on the design variable to fit an optimal solution from the optimization model. This method can theoretically solve to the optimal solution, but the accuracy of the optimal solution depends on the test samples, and good solving accuracy requires a large number of test samples, resulting in extremely low efficiency. SUMMARY

[0009] To solve the above problems in the prior art, the application provides an optimization method for a battery pack box structure, which can improve optimization efficiency, effectively improve product development efficiency, and shorten the development cycle.

[0010] To solve the above technical problems, the application adopts the following technical solutions: an optimization method for a battery pack box structure, comprising:

[0011] establishing a CAE model of the battery pack box structure;

[0012] calculating the constraint modal of the battery pack box structure;

[0013] establishing a super-element model for the battery module and the upper cover respectively;

[0014] performing size optimization on the lower box based on the super-element model.

[0015] Further, the step of establishing the CAE model of the battery pack box structure comprises:

[0016] modeling the lower box using shell elements;

[0017] modeling the upper cover using shell elements;

[0018] modeling the battery module using equivalent homogeneous material body elements or using equivalent homogeneous battery cells plus glue.

[0019] Further, in the step of establishing the CAE model of the battery pack box structure, the battery module and the lower box are connected by beam elements and / or rbe2 elements and / or rbe3+solid+rbe3 elements, and the upper cover and the lower box are connected by beam elements and / or rbe2 elements.

[0020] Further, the step of calculating the constraint modal of the battery pack box structure comprises:

[0021] completely constraining the hangers of the battery pack box structure, and calculating the constraint modal of the battery pack box;

[0022] The calculation mode of the modal is set to the first 20 orders or 0-80Hz;

[0023] Further, AMSES is used to accelerate the solution when calculating the constrained modes of the battery pack case, and the AMPFACT parameter is set to 10.

[0024] Further, the step of respectively establishing super-element models for the battery module and the upper cover comprises:

[0025] The battery module and the upper cover are set as fixed quantities, and the battery module and the upper cover are respectively created as super-element models containing stiffness matrices and mass matrices by using CMS.

[0026] Further, the step of respectively creating the battery module and the upper cover as super-element models containing stiffness matrices and mass matrices by using CMS comprises:

[0027] The bolt connection points of the lower case are selected as boundaries, rbe2 elements respectively connecting the battery module and the upper cover to the lower case are selected, and one end of the selected rbe2 elements connected to the lower case is defined as ASET;

[0028] A working condition card of CMS is defined, the CMS type is defined as CBN, and the upper limit of the frequency of the super-element model is set to 200 Hz;

[0029] The format of the calculation result of the super-element model is defined as H3D;

[0030] The simulation software is defined to only output the model containing the super-element part, and the stiffness matrix and the mass matrix of the super-element model are obtained.

[0031] Further, the step of respectively creating the battery module and the upper cover as super-element models containing stiffness matrices and mass matrices by using CMS further comprises:

[0032] Units other than the super-element model of the upper cover and the super-element model of the battery module are defined as residual models, and the residual models reference the result file of the super-element model through a keyword ASSIGN;

[0033] The type of ASSIGN is defined as H3DDMIG;

[0034] The node numbers of the rbe2 elements connected to the residual model correspond to the node numbers of ASET in the super-element model one by one.

[0035] Further, before the step of performing size optimization on the lower case based on the super-element model, there is a step of verifying the rationality of the super-element model, and the step of verifying the rationality of the super-element model comprises:

[0036] Whether the error value of the corresponding stiffness matrix and mass matrix of the super-element model is less than or equal to 1% compared with the stiffness matrix and mass matrix of the model established by the non-super-element method is compared;

[0037] If the error value of the comparison result of the stiffness matrix and / or the mass matrix is greater than 1%, the frequency of the super unit model is adjusted to an error value less than or equal to 1%.

[0038] Further, the size optimization step of the lower box based on the super unit model comprises:

[0039] The thickness of each part of the lower box is defined as a variable;

[0040] The variable is defined as discrete, and the discrete value is 0.1;

[0041] The optimization target is set;

[0042] The first-order overall constraint mode of the battery pack box is defined as an optimization constraint condition;

[0043] Optimization solution, optimization solution of variables is carried out using simulation software, and the global iteration number is defined as 30 times.

[0044] Further, it further comprises an optimization result engineering step: combining process and cost factors for engineering processing, importing the results of the optimization solution into the CAD software and outputting the optimization scheme.

[0045] Further, it further comprises an engineering result performance verification step: building a model according to the optimization scheme and verifying the modal performance.

[0046] Further, the optimization method of the battery pack box structure is realized based on OptiStruct software or NASTRAN software.

[0047] The present application mainly has the following beneficial effects: the optimization method of the present application establishes a super unit model of the battery module and the upper cover, defines the battery module and the upper cover as a fixed amount, improves the optimization rate, shortens the product development cycle, and uses the constraint mode as the optimization constraint condition to simplify the complex working condition, improve the optimization efficiency and ensure the reliability of the optimization result. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 is a flow chart of the optimization method of the battery pack box structure of the embodiment of the present application;

[0049] Figure 2 is a schematic diagram of the lower box unit model of the embodiment of the present application;

[0050] Figure 3 is a modeling schematic diagram of the battery module of the embodiment of the present application;

[0051] Figure 4 is a schematic diagram of the upper cover, the battery module and the lower box connection part of the embodiment of the present application;

[0052] Figure 5 is a schematic diagram of a super cell model of an embodiment of the present application;

[0053] Figure 6 is a schematic diagram of a lower box definition variable of an embodiment of the present application. DETAILED DESCRIPTION

[0054] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0055] Referring to Figure 1 An optimization method of a battery pack box structure, the optimization method is realized based on OptiStruct software or NASTRAN software, and the embodiment is described based on OptiStruct software, and the optimization method comprises the following steps:

[0056] S100, a CAE model of the battery pack box structure is established based on OptiStruct software, referring to Figure 2 In order to facilitate the creation of the super cell model of the upper cover and the battery module, the specific steps include the following steps:

[0057] a) the lower box of the punched sheet metal and the extruded profile structure is modeled using shell elements, and different thickness parameters are defined according to the actual thickness of each part of the lower box;

[0058] b) the upper cover is modeled using shell elements, and different thickness parameters are defined according to the actual thickness of each part of the upper cover;

[0059] c) the battery module is modeled using body elements of equivalent homogeneous material, referring to Figure 3 It can also be modeled in the form of equivalent homogeneous battery cells and adhesive, wherein the adhesive can be modeled using body elements with common nodes or rbe3+solid+rbe3, and it should be noted that the equivalent property parameters of the battery cells or the battery module need to be obtained by test benchmarking or theoretical calculation;

[0060] d) the battery module and the lower box can be connected using corresponding modeling methods according to different structural connection forms, wherein the bolt connection can be modeled using beam elements and / or rbe2 elements and / or rbe3+solid+rbe3;

[0061] e) the bolt connection between the upper cover and the lower box can be modeled using beam elements and / or rbe2 elements, referring to Figure 4As shown, in the present embodiment, the connection between the upper cover and the lower box body and between the battery module and the lower box body is modeled by beam elements and / or rbe2 elements and / or rbe3+solid+rbe3, which facilitates the creation of a super-element model and improves the optimization efficiency.

[0062] S200 calculates the constraint modal of the battery pack box body structure, which includes the following steps:

[0063] Each hanger point of the fully constrained battery pack box body structure is calculated, the constraint modal of the battery pack box body is calculated, and the solution mode of the calculation modal can be set to the first several orders or a certain frequency range, which is usually the first 20 orders or 0-80Hz. Due to the large number of elements of the battery pack box body structure, in order to improve the calculation efficiency, AMSES can be used to accelerate the solution when calculating the constraint modal of the battery pack box body. In order to improve the calculation accuracy, the AMPFACT parameter needs to be turned on when using AMSES to accelerate the solution, and the AMPFACT parameter is set to 10. The present application uses the constraint modal as the optimization constraint condition, which can simplify the complex working conditions and improve the optimization efficiency, while ensuring the reliability of the optimization results.

[0064] S300 establishes a super-element model for the battery module and the upper cover respectively, referring to Figure 5 As shown, it should be noted that the battery pack box body structure includes an upper cover, a battery module and a lower box body. In the design and development process, the modal of the upper cover needs to be investigated separately, and the battery module is optimized as a subsystem level. Therefore, the overall modal optimization of the present embodiment is usually only for the lower box body. Therefore, the upper cover and the battery module are not optimized in the present scheme, and the upper cover and the battery module are fixed during the optimization process. CMS is used to create a super-element model containing stiffness matrix and mass matrix for the battery module and the upper cover, so as to reduce the number of iterations in the convergence process of finite element solution calculation and improve the optimization efficiency. The steps of creating a super-element model include:

[0065] The bolt connection points of the lower box body are boundaries, the rbe2 elements connected between the battery module, the upper cover and the lower box body are selected, and one end of the selected rbe2 element connected with the lower box body is defined as ASET.

[0066] The working condition card of CMS is defined. Since the battery pack box body structure only has structural elements, the CMS type can be defined as CBN, and the upper limit frequency of the super-element model is set to 200Hz.

[0067] The format of the calculation result of the super-element model is defined as H3D.

[0068] It is defined that the OptiStruct software only outputs the model containing the super-element part, and the stiffness matrix and mass matrix results of the super-element model are obtained.

[0069] The residual model is defined in addition to the upper cover super cell model and the battery module super cell model, the residual model references the result file of the super cell model through the keyword ASSIGN, and a complete battery pack box model can be formed;

[0070] The type of the ASSIGN is defined as H3DDMIG;

[0071] The rbe2 node number of the residual model is one-to-one corresponding to the node number of the ASET in the super cell model; in order to ensure the maintainability of the model, the node number segment of the ASET should be distinguished from the node number segment of the rest, for example, the node number segment of the ASET is defined as four digits, and the node number segment of the rest is defined as eight digits.

[0072] S400 verifies the rationality of the super cell model, and the specific steps are as follows:

[0073] The modal of the residual model is calculated by OptiStruct, at this time the residual model references the stiffness matrix and the mass matrix of the super cell model, in theory the stiffness matrix and the mass matrix of the residual model are consistent with the stiffness matrix and the mass matrix of the model established by the non-super cell method, and the calculation results should also be consistent, but due to the error of the intercepted modal of the super cell model, there may be a small error when using the super cell method, therefore, when comparing the stiffness matrix and the mass matrix of the super cell model with the stiffness matrix and the mass matrix of the model established by the non-super cell method, the error of the value of the first ten order modes is less than or equal to 1%, which is considered to be within the acceptable range, if the error of the comparison result of the stiffness matrix and / or the mass matrix is greater than 1%, adjust the intercepting frequency of the super cell model, and check whether the ASET is defined incorrectly at the same time, until the error is less than or equal to 1% to proceed to the next step of optimization.

[0074] S500, if the super cell model is reasonable, the size optimization of the lower box is carried out based on the super cell model, and the specific steps are as follows:

[0075] a) define each part of the thickness of the lower box as a variable, different structures of different lower boxes are different, in this embodiment, only the thickness of the lower box is defined as variable a~variable p; Figure 6 As an example, in this embodiment, the thickness of each part of the lower box is defined as variable a~variable p;

[0076] b) define the variable solution domain, in this embodiment, each design variable is a uniform thickness, according to the extrusion molding process requirement, the variable a~variable p of the wall thickness of each part of the lower box is 1mm-10mm, at the same time, the sealing requirement between the lower box and the upper cover needs to be considered, the stiffness of the variable b at the matching part of the lower box and the upper cover needs to be ensured, therefore the variable b is 2mm-10mm, and each variable is defined as a discrete variable with a discrete value of 0.1;

[0077] c) Set optimization target, in this embodiment, the target is to achieve a strong quantitative design, and the target is to minimize the mass of the lower box. Of course, different optimization targets can be set according to actual conditions;

[0078] d) Constraint condition, define the first-order overall constraint mode of the battery pack box as the optimization constraint condition. The constraint definition value can be defined according to the actual situation or the performance index obtained by decomposing the designed vehicle. It can also be selected according to the actual situation whether modal vibration mode tracking is needed;

[0079] e) Optimization solution, OptiStruct is used for optimization solution of variables. In order to improve the solution accuracy, the global iteration number can be set to 30 times.

[0080] S600 optimization result engineering, according to the optimization scheme, engineering processing is carried out combined with process, cost and other factors. The results of optimization solution are imported into CAD software and the optimization scheme is output.

[0081] S700 performance verification of engineering result, since there is a slight difference between the data after engineering processing and the data of the optimization result, in order to ensure the rigor of the optimization scheme, a model needs to be built according to the optimization scheme and modal performance verification needs to be carried out. Since the scheme optimization does not design the part of the super element model, in order to provide efficiency, the performance verification of this step only needs to model the lower box. If the verification result meets the performance requirement, the final optimization scheme can be output. If the verification result does not meet the performance requirement, the optimization constraint condition (boundary condition) needs to be adjusted and the optimization calculation needs to be carried out again until the verification result meets the performance requirement and the final optimization scheme can be output.

[0082] It should be noted that the AMSES (Automated Multi-level Sub-structuring Eigenvalue Solution) method described in all the above embodiments is to decompose and reduce the model with millions of degrees of freedom layer by layer into hundreds of subsystem modalities with consistent modal space as the original modal space through matrix transformation. Such a way not only can quickly and effectively calculate the subsystem modalities, but also can effectively improve the efficiency of response calculation in the modal space, reduce the occupation of hard disk space and read-write, so as to shorten the time of modal calculation and frequency response calculation.

[0083] It should be noted that the CMS (Component Mode Synthesis) described in all the above embodiments is commonly used for modal analysis in the industry, such as free modalities and constraint modalities. The CMS method can be used to create a super element model. CMS is to split all matrices into sub-matrices through matrix condensation, and then combine them through certain rules to improve the calculation efficiency.

[0084] The above is the preferred embodiment of the present application, it should be noted that for those skilled in the art, without departing from the principles of the present application, can also make several improvements and refinements, these improvements and refinements are also considered the scope of protection of the present application.

Claims

1. A method of optimizing a battery pack enclosure structure, comprising: The method comprises the following steps: establishing a CAE model of the battery pack box structure; calculating the constraint modal of the battery pack box structure; establishing a super-element model for the battery module and the upper cover respectively; performing size optimization on the lower box based on the super-element model; the step of establishing a super-element model for the battery module and the upper cover respectively comprises: setting the battery module and the upper cover as fixed quantities, and using CMS to create a super-element model containing a stiffness matrix and a mass matrix for the battery module and the upper cover respectively.

2. The method of optimizing a battery pack enclosure structure of claim 1, wherein, the step of establishing a CAE model of the battery pack box structure comprises: using shell elements to model the lower box; using shell elements to model the upper cover; using equivalent homogeneous material body elements to model the battery module or using equivalent homogeneous battery cells plus adhesive modeling.

3. The method of optimizing a battery pack enclosure structure of claim 2, wherein, In the step of establishing a CAE model of the battery pack box structure, the battery module and the lower box are connected by beam elements and / or rbe2 elements and / or rbe3+solid+rbe3 elements, and the upper cover and the lower box are connected by beam elements and / or rbe2 elements.

4. The method of optimizing a battery pack enclosure structure of claim 1, wherein, the step of calculating the constraint modal of the battery pack box structure comprises: completely constraining the hangers of the battery pack box structure, and calculating the constraint modal of the battery pack box; the solution mode of the modal calculation is set to the first 20 orders or 0-80Hz.

5. The method of optimizing a battery pack enclosure structure of claim 4, wherein, AMSES is used to accelerate the solution when calculating the constraint modal of the battery pack box, and the AMPFACT parameter is set to 10.

6. The method of optimizing a battery pack enclosure structure of claim 1, wherein, In the step of using CMS to create a super-element model containing a stiffness matrix and a mass matrix for the battery module and the upper cover respectively, the following steps are included: selecting the rbe2 elements connecting the battery module and the upper cover to the lower box as boundaries, and defining the end of the selected rbe2 elements connected to the lower box as ASET; defining the working condition card of CMS, and setting the CMS type as CBN, and setting the upper limit frequency of the super-element model as 200Hz; defining the format of the calculation results of the super-element model as H3D; defining the simulation software to output only the model containing the super-element part, and obtaining the stiffness matrix and mass matrix results of the super-element model.

7. The method of optimizing a battery pack enclosure structure of claim 6, wherein, In the step of using CMS to create a super-element model containing a stiffness matrix and a mass matrix for the battery module and the upper cover respectively, the following steps are included: defining the elements other than the super-element model of the upper cover and the super-element model of the battery module as residual models, and referencing the result file of the super-element model by the keyword ASSIGN for the residual models; defining the type of ASSIGN as H3DDMIG; the node numbers of the rbe2 elements connected to the residual model correspond to the node numbers of ASET in the super-element model one by one.

8. The method of optimizing a battery pack enclosure structure of claim 1, wherein, Before the step of performing size optimization on the lower box based on the super-element model, there is a step of verifying the rationality of the super-element model, which comprises the following steps: comparing the error values of the stiffness matrix and the mass matrix of the super-element model with the stiffness matrix and the mass matrix of the model established by the non-super-element method to determine whether the error values are less than or equal to 1%; if the error values of the stiffness matrix and / or the mass matrix are greater than 1%, adjust the cut-off frequency of the super-element model to less than or equal to 1%.

9. The method of optimizing a battery pack enclosure structure of claim 1, wherein, The size optimization step of the lower box based on the super unit model comprises: The thickness of each part of the lower box is defined as a variable; The variable is defined as discrete, and the discrete value is 0.1; Set the optimization goal; Define the first-order overall constraint mode of the battery pack box as the optimization constraint condition; Optimization solution, optimization solution of variables is carried out using simulation software, and the global iteration number is defined as 30 times.

10. The method of optimizing a battery pack enclosure structure of claim 1, wherein, It also includes an optimization result engineering step: combining process and cost factors for engineering processing, importing the results of the optimization solution into CAD software and outputting the optimization scheme.

11. The method of optimizing a battery pack enclosure structure of claim 1, wherein, It also includes an engineering result performance verification step: building a model according to the optimization scheme and verifying the modal performance.

12. The method of optimizing a battery pack enclosure structure of any one of claims 1-11, wherein, The optimization method is realized based on OptiStruct software or NASTRAN software.

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