Abstract
To ensure the safety and reliability of the power battery pack in electric vehicles (EVs), this study employs finite element theory to analyze its structural characteristics. By constructing a 3D model, optimizing grid division, and setting boundary conditions, we simulate the static strength of the battery pack under five typical working conditions: braking, acceleration, left/right turning, and climbing. The results reveal the maximum equivalent stress and yield strength, verifying the structural feasibility and safety. Additionally, optimization suggestions for enhancing the stiffness of the battery pack cover are proposed, providing theoretical guidance for further structural design improvements.
1. Introduction
With the growing environmental awareness and supportive policies for new energy vehicles, the global EV industry has witnessed rapid development. The power battery pack, as a core component of EVs, is mounted on the vehicle frame and subjected to complex extreme conditions during operation. The battery pack casing and lifting lugs endure various acceleration impacts and reciprocating loads, potentially leading to safety hazards due to insufficient strength, stiffness, or fatigue damage . Therefore, analyzing the structural performance of the battery pack to improve its mechanical properties and service life is crucial for ensuring operational safety and reliability.
This study utilizes finite element simulation to evaluate the structural characteristics of the battery pack, aiming to provide theoretical and technical support for modeling, simulation, and structural optimization of EV battery packs.
2. Finite Element Model Construction of the Battery Pack
2.1 Finite Element Method Solving Steps
The finite element analysis (FEA) process involves three main stages:
2.1.1 Structural Discretization
The mechanical structure is divided into finite elements connected at nodes to form a discrete model. This model represents the original structure, with the aggregate of elements enabling accurate mechanical behavior simulation .
2.1.2 Element Analysis
a. Displacement Mode Selection: A displacement function describes the relationship between displacements at each point within an element and their positions, expressed as:\(y = \sum_{i=1}^{n} \alpha_{i} \varphi_{i}\) where \(\alpha_{i}\) are undetermined coefficients, and \(\varphi_{i}\) are coordinate-related functions .
b. Element Stiffness Equation Establishment: Based on the displacement mode and element type, the element stiffness equation is formulated as:\(k^{e} \sigma^{e} = F^{e}\) Here, e denotes the element number, \(\sigma^{e}\) is the node position vector, \(F^{e}\) is the node force vector, and \(k^{e}\) is the element stiffness matrix .
c. Equivalent Node Force Calculation: Surface forces, concentrated forces, or volume forces acting on element boundaries are converted into equivalent node forces for separate calculation .
2.1.3 Global Analysis
After discretization and element analysis, the global finite element equation is derived based on boundary and equilibrium conditions:\(K\sigma = F\) where K is the total stiffness matrix, \(\sigma\) is the node displacement vector, and F is the load vector .
2.2 Construction Process of the Battery Pack FEA Model
The construction process of the battery pack finite element model is outlined in Table 1, including parameter measurement, geometric simplification, material property setting, meshing, and boundary condition definition .
Table 1. Construction Process of the Battery Pack FEA Model
| Step | Description |
|---|---|
| Structural parameter measurement | Acquire dimensions and mass of the battery pack |
| Geometric model simplification | Remove non-critical features for computational efficiency |
| Material property setting | Assign elastic modulus, Poisson’s ratio, density, etc. |
| Meshing | Divide the model into finite elements with appropriate density |
| Boundary condition definition | Set fixed supports and load cases |
| Mesh quality optimization | Refine meshes to ensure calculation accuracy |
3. Basic Parameters and Material Properties of the Battery Pack
3.1 Basic Geometric and Mass Parameters
The battery pack’s basic parameters are listed in Table 2, showing its dimensions, total mass, and electrical specifications .
Table 2. Basic Parameters of the EV Power Battery Pack
| Parameter | Value |
|---|---|
| Length (mm) | 770 |
| Width (mm) | 560 |
| Height (mm) | 275 |
| Total mass (kg) | 158 |
| Nominal capacity (A·h) | 150 |
| Nominal voltage (V) | 76.8 |
3.2 Material Properties of Components
Table 3 details the material properties of key components, including elastic modulus, Poisson’s ratio, density, shear modulus, and yield strength . Most components (e.g., lifting lugs, cover, casing, and 支架) are made of structural steel, while the packing belt uses stainless steel.
Table 3. Material Properties of Battery Pack Components
| Component | Material | Elastic Modulus (GPa) | Poisson’s Ratio | Density (kg/m³) | Shear Modulus (GPa) | Yield Strength (MPa) |
|---|---|---|---|---|---|---|
| Lifting lug | Structural steel | 201 | 0.30 | 7850 | 76 | 250 |
| Cover | Structural steel | 201 | 0.30 | 7850 | 76 | 250 |
| Casing | Structural steel | 201 | 0.30 | 7850 | 76 | 250 |
| Bracket | Structural steel | 201 | 0.30 | 7850 | 76 | 250 |
| Packing belt | Stainless steel | 193 | 0.31 | 7750 | 73 | 210 |
3.3 Model Simplification Strategies
To facilitate FEA, the model simplifies the contact surfaces, tension, and friction coefficients between battery cells and brackets. Battery blocks are equivalent to concentrated mass points bolted to the casing, ensuring computational efficiency while maintaining structural accuracy .
4. Static Characteristics Analysis of the Battery Pack
4.1 Static Strength Simulation under Self-Gravity
In the Mechanical module, a gravitational acceleration of \(9.8~m/s^{2}\) (negative Z-axis direction) is applied, with fixed constraints on the six lifting lug mounting holes. The simulation results show:
- Maximum Displacement: 2.6 mm at the center of the casing cover, indicating insufficient self-stiffness of the cover that requires optimization .
- Stress Distribution: The front and rear brackets bear significant forces due to the weight of battery modules. The maximum stress (19.14 MPa) occurs at the end near the air duct, with all components remaining in elastic deformation (plastic strain = 0) -.
4.2 Simulation of Typical Static Working Conditions
The battery pack’s loading conditions during five typical EV operations (braking, acceleration, left/right turning, and climbing) are specified in Table 4, where \(g = 9.8~m/s^{2}\) .
Table 4. Loading Conditions for Typical Working Conditions
| Working Condition | X (Driving Direction) | Y (Left Perpendicular to Driving) | Z (Upward Perpendicular to Driving) |
|---|---|---|---|
| Emergency braking on uneven road | +5g | — | -2g |
| Starting acceleration on uneven road | -3g | — | -2g |
| Left turning on uneven road | — | +3g | -2g |
| Right turning on uneven road | — | -3g | -2g |
| Climbing on uneven road | -g | — | -2g |
4.2.1 Emergency Braking Condition
- Maximum Stress: 54.841 MPa at the connection between the left front lifting lug and the casing.
- Maximum Deformation: 0.653 mm at the center of the casing cover, caused by horizontal and vertical inertial accelerations .
4.2.2 Starting Acceleration Condition
- Maximum Stress: 34.853 MPa at the connection between the left rear lifting lug and the casing.
- Maximum Deformation: 0.655 mm at the cover center, resulting from backward and vertical inertial forces .
4.2.3 Left Turning Condition
- Maximum Stress: 0.042 MPa at the connection between the front suspension lug and the casing.
- Deformation: 0.0007 mm at the cover center, due to lateral and vertical accelerations .
4.2.4 Right Turning Condition
- Maximum Stress: 0.045 MPa at the rear lifting lug.
- Deformation: 0.0006 mm at the cover center, caused by lateral and vertical forces .
4.2.5 Climbing Condition
- Maximum Stress: 0.026 MPa at the connection between the right front cover and the casing.
- Deformation: 0.0006 mm at the cover center, resulting from forward and vertical accelerations .
4.3 Comprehensive Evaluation of Static Analysis
The static analysis under typical conditions reveals that the battery pack withstands all loads with a maximum deformation of 0.655 mm, meeting the design requirements. This confirms the structure’s sufficient strength and safety for EV operations .
5. Optimization Suggestions for the Battery Pack Structure
Based on the simulation results, the casing cover exhibits insufficient stiffness, as indicated by significant central deformation. To improve structural performance, we propose:
- Reinforcing the Cover Structure: Adding rib plates or increasing the thickness of the cover to enhance its rigidity.
- Material Optimization: Using high-strength alloys for critical components (e.g., lifting lugs and brackets) to reduce stress concentrations.
- Design Refinement: Optimizing the connection between the cover and casing to distribute loads more evenly.
6. Conclusion
In this study, we established a finite element model of an EV power battery pack, simulating its static strength under five typical working conditions. The key findings include:
- The maximum equivalent stress and yield strength under each condition were obtained, verifying the structural feasibility and safety.
- The casing cover’s central deformation under self-gravity and dynamic loads highlights the need for stiffness enhancement.
- The battery pack meets design requirements, demonstrating sufficient strength for practical EV applications.
These conclusions provide theoretical and technical support for optimizing the structural design of EV power battery packs, contributing to safer and more reliable battery systems in electric vehicles.