CN114861480A - Method for optimizing reliability of weld layout of electric vehicle chassis - Google Patents

Abstract

The invention discloses a method for optimizing the reliability of the weld layout of an electric vehicle chassis, which relates to the field of the structural design and manufacture integration of the electric vehicle chassis and is characterized by comprising the following steps: step 1: initializing design conditions and optimization parameters; and 2, step: performing unit density interpolation modeling; and 3, step 3: structural global stress constraint modeling; and 4, step 4: thermal deformation constraint modeling in the welding process; and 5: modeling topology optimization; step 6: solving a design response; and 7: analyzing the sensitivity; and 8: optimizing and solving; and step 9: judging a convergence condition; step 10: and (5) optimizing the result and performing post-processing. The invention realizes the cooperative optimization of the layout of the chassis frame and the welding seam, obtains the optimized configuration which is light and meets the reliability requirements of load bearing safety and the like under the condition of considering the stress distribution of the whole structure and the welding thermal deformation, is beneficial to reducing the rejection rate, improving the mass production efficiency, reducing the design iteration times, shortening the development period and reducing the development cost.

Description

Method for optimizing reliability of weld layout of electric vehicle chassis

Technical Field

The invention relates to the field of structural design and manufacture integration of an electric vehicle chassis, in particular to a method for optimizing the layout reliability of welding seams of the electric vehicle chassis.

Background

With the increasingly prominent energy and environmental protection problems, electric vehicles are gradually favored by consumers due to their advantages of low pollution and low noise. At present, most electric automobile manufacturers adopt a 'pure electric development' mode, namely, a vehicle body structure is developed according to the appearance characteristics of three electric systems (a motor, a battery and an electric control). The battery pack is connected to the automobile body through the mounting device, and the 'mounting type' battery pack is only designed for protecting the battery core, has limited contribution degree to the bearing performance of the whole automobile, occupies nearly 30% of the total weight, seriously restricts the further promotion of the endurance mileage of the electric automobile, and has the problem of industrial pain due to the light structure of the electric automobile.

Compared with a 'hanging type' battery pack, a brand new development mode is advocated by a recently-emerging slide plate type chassis, namely an integrated design of the battery pack and the chassis. The development idea is as follows: but the chassis frame structure of direct mount electric core unit is designed, and electric core participates in as frame structure's partly and bears, and this thinking is hoped to further promote the performance in service and the lightweight degree of chassis structure, is favorable to promoting electric core loading capacity, increases electric automobile continuation of the journey mileage. The novel chassis frame is required to provide enough strong protection for the battery cell and ensure the bearing safety performance of the whole vehicle, so that the sliding plate type chassis frame has more and more complex cross transverse and longitudinal reinforcing beam structural forms compared with the traditional chassis structure, more welding procedures are required to complete chassis assembly and connection, and new requirements are provided for the control of the manufacturing quality of the electric vehicle chassis structure. The local strength attenuation and the local thermal deformation generated in the welding process are considered by developers in the design stage, and the actual shape of the chassis structure is ensured to meet the design expectation to the maximum extent, so that the high-quality manufacturing of products is ensured, and the assembly precision and the production efficiency are improved.

In order to ensure that the strength and the welding thermal deformation of a welding seam meet design expectation and assembly requirements, the traditional method is to develop a chassis frame structure welding experiment on the basis of primary design, measure the welding thermal deformation, develop a tensile-shear mechanical property test, determine the actual strength of the welding seam, modify a design scheme or improve technological parameters such as laser power and welding sequence according to actual assembly precision limit and mechanical property requirements. The method depends on engineering experience, cannot fully ensure the bearing safety performance and the manufacturing precision of the structure, and has long development period, high cost and poor structure reliability. At present, the chassis frame structure welding seam layout optimization method based on engineering experience trial and error and repeated optimization iteration cannot ensure that the structural design strength of the electric vehicle chassis frame meets the safety requirement, and is difficult to control the thermal deformation in the structure welding process, so that the development cycle of the electric vehicle chassis platform is long, the manufacturing cost is high, the structural bearing safety performance and the light weight degree are required to be further improved, and the reliability is poor.

Therefore, aiming at the problems of long development period and high design cost in the prior art, the technical personnel in the field are dedicated to developing a reliability optimization method for the welding seam layout of the chassis of the electric vehicle, realizing the cooperative optimization of the layout of the chassis frame and the welding seam, and obtaining an optimized configuration which is light and meets the reliability requirements of load bearing safety and the like under the condition of considering the stress distribution of the whole structure and the welding thermal deformation.

Disclosure of Invention

In view of the above defects in the prior art, the technical problem to be solved by the invention is to realize cooperative optimization of the layout of the chassis frame and the welding seam of the electric vehicle, and obtain an optimized configuration which is light and meets the reliability requirements of load bearing safety and the like under the condition of considering the stress distribution of the whole structure and the welding thermal deformation.

In order to achieve the purpose, the invention provides a method for optimizing the weld layout reliability of an electric vehicle chassis, which is characterized by comprising the following steps:

step 1, initializing design conditions and optimization parameters, defining a design domain, a non-design domain, load and boundary conditions, establishing a finite element model, and initializing parameters and design variables;

step 2, establishing a parameterized model of layout density and rigidity of the frame and the welding seam;

step 3, establishing a structural global stress constraint model;

step 4, establishing a thermal deformation constraint model in the welding process;

step 5, topological optimization modeling is carried out, a topological optimization model of the welding seam layout of the electric vehicle chassis is established, and an objective function and a constraint function are determined, wherein the objective function is the minimum structure flexibility, and the constraint function comprises a structure overall mass constraint function, a structure overall stress constraint function and a welding process thermal deformation constraint function;

step 6, solving the finite element model to obtain each design response;

7, analyzing the sensitivity of the target function and the sensitivity of the constraint function;

step 8, optimizing and solving, namely solving the electric vehicle chassis welding seam layout topological optimization model and updating the design variables;

and 9, judging a convergence condition, and if the convergence condition is not met, repeating the steps 5 to 8 until the convergence condition is met.

Further, in the step 1, the design domain is a chassis frame structure of the electric vehicle, and the non-design domain is a battery core and a motor of the electric vehicle.

Further, in the step 2, the parameterized models of the layout density and the rigidity of the frame and the welding seam are modeled by using unit density interpolation, the number of the design variables is set to be 2, and the step 2 further includes:

2.1, based on a density filtering formula and a Heaviside projection format, respectively converting 2 design variables into a base region density field, a first partition density field and a second partition density field by applying a two-step filtering method and calculating differences; sequentially using geometric mean and projection to convert the first partition density field and the second partition density field into a weld structure, and constructing a uniform expression formula of unit density by using the base region density field and the density field of the weld structure;

and 2.2, establishing a parameterized model of the layout density and rigidity of the frame and the welding seam by adopting a solid isotropic material with punishment method (SIMP), and integrating element density interpolation into finite element analysis.

Further, in the step 3, the structural global stress constraint model is a structural global stress constraint which is constructed based on a p-norm method with a unit gaussian integral point as a reference.

Further, the step 4 further includes establishing a welding process simulation model based on an inherent strain method, where the welding process thermal deformation constraint model is a welding process thermal deformation constraint established based on a p-norm.

Further, the step 6 further includes obtaining structural deformation, stress and structural welding thermal deformation under the service working condition respectively by solving the finite element model and the welding process simulation model based on structural density information in the current optimization iteration step, and further calculating structural flexibility, structural overall mass constraint, structural global stress constraint and welding process thermal deformation constraint.

Further, in the step 7, the sensitivity analysis refers to deriving a sensitivity formula of the objective function and the constraint function to the design variable based on a chain rule, and solving a sensitivity value in each optimization iteration step.

Further, in the step 8, a moving asymptote algorithm (MMA) is used for solving the topological optimization model of the weld layout of the electric vehicle chassis.

Further, in the step 9, the convergence condition means that the change rate of the objective function is lower than 0.2% in the current 5 iterations, and the projection sharpness of the Heaviside function reaches a preset maximum value with the optimization iteration.

Further, the method for optimizing the reliability of the weld layout of the electric vehicle chassis further comprises the following steps:

and step 10, performing post-processing on the optimization result, and reserving units with the pseudo density value larger than 0.5 in the optimization result based on a projection dichotomy to form a clear optimization result.

Adopt above-mentioned technical scheme to carry out chassis frame and advantage of welding seam overall arrangement collaborative optimization lie in:

1. according to the invention, stress constraint is added in the topological optimization model of the welding line layout of the electric vehicle chassis, so that a structure meeting the bearing safety performance of the structure is obtained, the bearing reliability of the structure is improved, the welding strength can be ensured to meet the requirement in the design stage, and the bearing safety of the optimized structure is ensured.

2. According to the invention, welding thermal deformation constraint is integrated in the welding seam layout topological optimization model, welding thermal deformation is controlled in the design stage, thermal deformation of an optimization result can be controlled, the assembly reliability of the structure is improved, the situation that smooth assembly cannot be realized due to overlarge structural thermal deformation is avoided, the rejection rate is reduced, and the mass production efficiency is improved.

3. The invention can realize the layout collaborative design of the chassis frame and the welding line, reduce the design iteration times, shorten the development period and reduce the development cost.

The conception, the specific structure and the technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, the features and the effects of the present invention.

Drawings

FIG. 1 is a flow chart of a method for optimizing weld layout reliability of an electric vehicle chassis according to a preferred embodiment of the invention;

FIG. 2 is a schematic diagram of a parameterized modeling of a chassis frame and a weld structure of an electric vehicle according to a method for optimizing the reliability of the weld layout of an electric vehicle chassis in accordance with a preferred embodiment of the present invention;

FIG. 3 is a schematic diagram of the structural design domain, load and boundary conditions of the chassis of the electric vehicle of the method for optimizing the weld layout reliability of the chassis of the electric vehicle according to the preferred embodiment of the present invention;

FIG. 4 is a schematic diagram of a layout topology optimization result of a weld joint of an electric vehicle chassis according to a method for optimizing the layout reliability of the weld joint of the electric vehicle chassis in accordance with a preferred embodiment of the present invention;

the method comprises the following steps of 1-design domain, 2-fixing point, 3-battery cell, 4-frame and 5-welding line.

Detailed Description

The technical contents of the preferred embodiments of the present invention will be more clearly and easily understood by referring to the drawings attached to the specification. The present invention may be embodied in many different forms of embodiments and the scope of the invention is not limited to the embodiments set forth herein.

In the drawings, structurally identical elements are represented by like reference numerals, and structurally or functionally similar elements are represented by like reference numerals throughout the several views. The size and thickness of each component shown in the drawings are arbitrarily illustrated, and the present invention is not limited to the size and thickness of each component. The thickness of the components may be exaggerated where appropriate in the figures to improve clarity.

The embodiments of the invention will be described in further detail with reference to the following drawings and examples:

as shown in fig. 1, a flowchart of an optimization method for reliability of weld layout of an electric vehicle chassis according to the present invention implements the following steps:

step 1: as shown in fig. 3, a design domain with dimensions of 280 × 110 is defined, and a finite element model is established, wherein the node shown in the figure is a fixed point, and a horizontal direction load F applied to the left side is 1000N; the optimization parameters are initialized as follows: upper limit of mass as a whole of m ^* 800kg, global stress upper limit σ ^* 685MPa, and the upper limit of welding thermal deformation

The density filtration radius is R ₁ ＝16，R ₂ ＝16，R ₃ ＝6，R ₄ 6, modulus of elasticity E of vehicle frame material ₁ 210GPa, poisson ratio υ ₁ 0.33, weld modulus of elasticity E ₂ 168GPa, Poisson's ratio upsilon ₂ 0.33, Heaviside function sharpness maximum β _max ＝64。

Step 2: as shown in FIG. 2, for the first design variable m and the second design variable n, the two-step filtering method is used to determine the base region density field for controlling the existence of material

A second partition density field psi of the control material partition is obtained, and the difference between the two is used for further obtaining a second partition density field psiA region density field mu for the density-filtered smooth base region density field

And

and performing gradient normalization treatment, calculating the geometric mean value of the two gradient density fields, and performing primary projection to obtain the interface density field tau of the weld structure.

From this, the cell density field ρ _e The unified expression of (a) is as follows:

where ρ is ₁ Is the density of the frame material, rho ₂ For weld material density, e represents the cell number.

Adopting a Solid Isotropic Material Process (SIMP) with punishment to establish a parameterized model of layout density and rigidity of the frame and the welding line and a unit elastic modulus E _e The relationship to the density field is as follows:

wherein, to avoid matrix singularity, the minimum value of the elastic modulus E _min ＝10 ^-9 GPa, penalty factor p ═ 3.

And step 3: solving the von Mises stress value of each unit based on the Gaussian integration point. The global stress constraint controls the stress distribution of the structure by limiting the unit with the maximum stress value, and the structure global stress constraint function l is composed of the p norm of the unit stress:

wherein the p-norm parameter is set to p _l ＝8，σ _mi Von Mise representing the ith units stress value, σ ^* Represents the maximum von Mises stress value allowed by the safety limit of the welding seam material.

And 4, step 4: the thermal deformation constraint in the welding process is used for limiting the deformation amount generated by welding in the optimization result, so that the assembly precision of the structure is improved. First, the thermal deformation of each cell is calculated based on the intrinsic strain method, and then the deformation of the cell with the maximum thermal deformation is limited by thermal deformation constraint, the thermal deformation constraint function T being composed of the p-norm of the cell thermal deformation:

wherein the p-norm parameter is set to p _T ＝8，x _Ti Represents the welding thermal deformation of the ith node,

representing the maximum amount of welding deformation of the structure that is allowed during the assembly process.

And 5: establishing a topological optimization model of the welding seam layout of the electric vehicle chassis:

min:c＝U ^T KU

s.t.:G(m,n)≤m ^*

l(m,n)≤σ

m _e ,n _e ∈[0,1],e∈Ω

KU＝F

wherein c is total structural flexibility, G is overall mass constraint, l is global stress constraint, T is thermal deformation constraint in the welding process, displacement response is obtained by solving KU to F, K is a stiffness matrix, U is a displacement vector, F is a load vector, subscript e represents a unit number, and Ω represents a design space.

Step 6: based on the density information of the structure under the current optimization iteration step, a structure finite element model is solved, the displacement response U of the structure is obtained, the structure flexibility value c is further calculated, and the following constraint function response is calculated:

and (3) integral mass constraint G:

global stress constraint l:

thermal deformation constraint T in the welding process:

and 7: and calculating the analytic sensitivities of the target function c, the integral quality constraint function G, the global stress constraint function l and the thermal deformation constraint function T in the welding process to the design variables m and n based on a chain rule.

Step 8, step 9 and step 10: and (3) solving the topological optimization model of the welding line layout of the electric vehicle chassis by adopting a mobile asymptote algorithm MMA to obtain a topological optimization result meeting the lightweight index and the structural bearing performance, as shown in FIG. 4.

The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.

Claims (10)

1. The method for optimizing the weld layout reliability of the chassis of the electric vehicle is characterized by comprising the following steps of:

step 1, initializing design conditions and optimization parameters, defining a design domain, a non-design domain, load and boundary conditions, establishing a finite element model, and initializing parameters and design variables;

step 2, establishing a parameterized model of layout density and rigidity of the frame and the welding seam;

step 3, establishing a structural global stress constraint model;

step 4, establishing a thermal deformation constraint model in the welding process;

step 5, topological optimization modeling, namely establishing a topological optimization model of the weld layout of the electric vehicle chassis, and determining a target function and a constraint function, wherein the target function is the minimum structure flexibility, and the constraint function comprises a structure overall mass constraint function, a structure overall stress constraint function and a welding process thermal deformation constraint function;

step 6, solving the finite element model to obtain each design response;

7, analyzing the sensitivity of the target function and the constraint function;

step 8, optimizing and solving, namely solving the electric vehicle chassis welding seam layout topological optimization model and updating the design variables;

and 9, judging a convergence condition, and if the convergence condition is not met, repeating the steps 5 to 8 until the convergence condition is met.

2. The method for optimizing the reliability of the weld layout of the chassis of the electric vehicle as claimed in claim 1, wherein in the step 1, the design domain is a chassis frame structure of the electric vehicle, and the non-design domain is a battery core and a motor of the electric vehicle.

3. The method for optimizing the weld layout reliability of the chassis of the electric vehicle as claimed in claim 1, wherein in the step 2, the parameterized models of the frame and weld layout density and the stiffness are modeled by using unit density interpolation, the design variables are set to be 2, and the step 2 further comprises:

2.1, based on a density filtering formula and a Heaviside projection format, respectively converting the 2 design variables into a base region density field, a first partition density field and a second partition density field by applying a two-step filtering method and calculating differences; sequentially using geometric mean and projection to convert the first partition density field and the second partition density field into a weld structure, and constructing a uniform expression formula of unit density by using the base region density field and the density field of the weld structure;

and 2.2, establishing a parameterized model of the layout density and rigidity of the frame and the welding seam by adopting a solid isotropic material with punishment method (SIMP), and integrating element density interpolation into finite element analysis.

4. The method for optimizing the reliability of the weld layout of the electric vehicle chassis according to claim 1, wherein in the step 3, the structural global stress constraint model is a structural global stress constraint constructed based on a p-norm method with a unit gaussian integral point as a reference.

5. The method for optimizing reliability of weld layout of an electric vehicle chassis according to claim 4, wherein the step 4 further comprises establishing a welding process simulation model based on an inherent strain method, wherein the welding process thermal deformation constraint model is a welding process thermal deformation constraint established based on a p-norm.

6. The method for optimizing the reliability of the weld layout of the chassis of the electric vehicle as claimed in claim 5, wherein the step 6 further comprises obtaining structural deformation, stress and structural welding thermal deformation under the service condition by solving the finite element model and the welding process simulation model based on structural density information in the current optimization iteration step, and further calculating structural flexibility, structural overall mass constraint, structural global stress constraint and welding process thermal deformation constraint.

7. The method as claimed in claim 1, wherein in the step 7, the sensitivity analysis is to derive sensitivity formulas of the objective function and the constraint function for the design variables based on chain rules, and to solve the sensitivity value in each optimization iteration.

8. The method for optimizing the weld layout reliability of the electric vehicle chassis according to claim 1, wherein in the step 8, a moving asymptote algorithm (MMA) is adopted for solving the topological optimization model of the weld layout of the electric vehicle chassis.

9. The method as claimed in claim 1, wherein in the step 9, the convergence condition means that the change rate of the objective function is lower than 0.2% in the current 5 iteration steps, and the projection sharpness of the Heaviside function reaches a preset maximum value with the iteration of optimization.

10. The method for optimizing the layout reliability of the weld joints of the electric vehicle chassis according to claim 1, wherein the method for optimizing the layout reliability of the weld joints of the electric vehicle chassis further comprises the following steps:

and step 10, performing post-processing on the optimization result, and reserving units with the pseudo density value larger than 0.5 in the optimization result based on a projection dichotomy to form a clear optimization result.

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