In the rapidly evolving automotive industry, pure electric vehicles represent a pivotal shift toward sustainable mobility, with electric SUVs gaining significant traction due to their versatility and consumer appeal. Lightweighting is an essential strategy for enhancing the efficiency and performance of electric SUVs, as it directly impacts range, handling, and overall energy consumption. Among various components, the back door of an electric SUV is a critical area for lightweight design, as it contributes to structural integrity, noise-vibration-harshness (NVH) performance, and aerodynamics. Traditional metal back doors have been extensively studied, but composite materials offer promising alternatives for weight reduction without compromising strength. This paper focuses on the modal analysis and optimization of a composite back door for a pure electric SUV, utilizing finite element methods to achieve design targets while maintaining or reducing mass. The approach involves detailed modeling, simulation, and iterative optimization to address vibrational characteristics, ensuring that the back door meets stringent NVH requirements for electric SUVs, which lack engine noise to mask other sounds. By exploring composite materials and structural enhancements, this study aims to provide a framework for future developments in electric SUV back door design, emphasizing lightweight solutions that enhance driving comfort and durability.
The finite element modeling of the electric SUV back door begins with a comprehensive representation of its geometry and components. The back door assembly for this electric SUV includes an outer panel made of modified polypropylene PP+EPDM-T30 and an inner panel composed of long glass fiber-reinforced polypropylene PP-LGF40, with overall dimensions of 805 mm × 1323 mm × 105 mm. Additional elements such as hinges, windshield, reinforcement plates, buffer pads, seal strips, lock mechanisms, tail lights, and wiper motors are integrated into the model. Using HyperMesh software, the finite element model is constructed with a focus on accuracy and computational efficiency. Thin-walled components like the inner and outer panels, hinges, windshield, and reinforcement plates are discretized using shell elements (CQUAD4), with a mesh size of 3 mm × 3 mm to capture detailed stress distributions and vibrational behavior. For components like buffer pads and seal strips, which provide support when the back door is closed, spring-damper elements (CBUSH) are employed in local coordinate systems to simulate their effects. Non-structural attachments such as the lock, tail lights, and wiper motor are modeled as concentrated mass elements (CONM2) to account for their inertial contributions without detailing their geometry. Connections between parts are simulated using adhesives for bonding and rigid body elements (RBE2 and RBE3) for bolted joints and mass attachments, respectively. The final model comprises 147,172 elements and 143,325 nodes, with a total mass of 25.2 kg, adhering to quality standards for mesh integrity and simulation reliability. This detailed setup ensures that the model accurately represents the electric SUV back door for subsequent modal analysis, providing a foundation for evaluating its dynamic properties and identifying areas for improvement.
Modal analysis is a fundamental aspect of structural dynamics, particularly for electric SUV components, as it helps predict vibrational responses that can affect NVH performance. The trimmed modal analysis focuses on the back door in its fully assembled state, with constraints applied to mimic real-world conditions: hinges, buffer pads, and seal strips are fully constrained on the body side, and a local coordinate system is established at the lock hook to simulate engagement. The governing equation for modal analysis is derived from the eigenvalue problem, expressed as: $$(K – \omega_i^2 M) \phi_i = 0$$ where \( K \) is the stiffness matrix, \( M \) is the mass matrix, \( \omega_i \) is the natural frequency of the \( i \)-th mode, and \( \phi_i \) is the corresponding mode shape vector. This equation highlights the relationship between stiffness, mass, and vibrational characteristics, emphasizing that lower-frequency modes are more susceptible to excitation and resonance. For the electric SUV back door, the first few modes are of primary interest due to their higher energy content and potential impact on comfort. The initial simulation reveals a first-order bending mode at 23.2 Hz, which falls below the target of 25 Hz, indicating a risk of vibrational issues in the electric SUV. The mode shape shows a global bending deformation in the central region of the back door, suggesting areas of low stiffness that require reinforcement. This analysis underscores the importance of modal optimization for electric SUV back doors, as improvements can prevent seal leaks, reduce noise, and enhance overall vehicle quality. By leveraging software like MSC.Nastran for solving the finite element equations and HyperView for visualizing results, this study ensures a rigorous evaluation of the back door’s dynamic behavior, paving the way for targeted design enhancements.
To address the identified deficiencies in the electric SUV back door’s modal performance, three optimization schemes are proposed, each targeting the central region where stiffness is lacking. The goal is to elevate the first-order bending frequency to at least 25 Hz without increasing the mass, aligning with the lightweight objectives for electric SUVs. The optimization strategies involve structural modifications that enhance local stiffness through geometric adjustments and material redistribution. Below is a summary of the proposed schemes in table format, detailing the implementation measures and their intended effects on the electric SUV back door.
| Scheme Number | Implementation Measures | Description |
|---|---|---|
| 1 | Reduce the inner area of the central seal strip to form a beam-like structure | This approach modifies the seal region to act as a stiffening beam, improving overall bending resistance without adding material. |
| 2 | Add aluminum profile connections to enhance mid-lower stiffness | By incorporating lightweight aluminum elements, this scheme boosts stiffness in critical zones, though it requires careful mass management. |
| 3 | Optimize the structural form of the mid-lower section | This involves redesigning the inner panel geometry to distribute stiffness more effectively, leveraging composite material properties. |
Each scheme is evaluated through finite element simulations to assess its impact on modal frequencies and mass. The optimization process iteratively refines the designs, ensuring that the electric SUV back door meets performance targets while adhering to weight constraints. For instance, Scheme 1 focuses on creating a梁形结构 (beam-like structure) by adjusting the seal strip area, which minimally affects mass but can enhance stiffness. Scheme 2 introduces aluminum profiles, which are lightweight yet stiff, but must be optimized to avoid weight penalties. Scheme 3 involves a holistic redesign of the back door’s lower section, using the anisotropic properties of composites to achieve better modal characteristics. These approaches demonstrate the versatility of optimization techniques for electric SUV components, highlighting how computational tools can drive innovative solutions in automotive design.
The simulation results for the three optimization schemes are compared to the original design, with a focus on the first-order bending frequency and total mass. The table below summarizes the outcomes, illustrating how each scheme performs relative to the target of 25 Hz for the electric SUV back door. This comparison is crucial for selecting the most effective optimization strategy that balances modal improvement with lightweight goals.
| Scheme | First-Order Natural Frequency (Hz) | Total Mass (kg) | Remarks |
|---|---|---|---|
| Original | 23.2 | 25.2 | Baseline design, below target |
| 1 | 23.3 | 25.67 | Minor improvement, slight mass increase |
| 2 | 24.1 | 26.42 | Better frequency, but mass exceeds limit |
| 3 | 25.3 | 25.13 | Meets target, mass reduced |
As shown, Scheme 3 achieves the desired first-order bending frequency of 25.3 Hz while reducing the mass to 25.13 kg, making it the optimal choice for the electric SUV back door. The mode shapes for each scheme are visualized to confirm that the vibrational characteristics align with expectations; for example, Scheme 3 exhibits a more uniform deformation pattern, indicating enhanced stiffness in the critical regions. The success of Scheme 3 can be attributed to its innovative use of composite materials and geometric optimization, which redistributes stiffness without adding weight. This outcome underscores the importance of integrated design and simulation in developing high-performance components for electric SUVs, where every gram saved contributes to overall efficiency. Furthermore, the iterative optimization process, guided by finite element analysis, ensures that the final design is both practical and cost-effective, ready for implementation in mass production. The robustness of this approach is validated through real-world testing on electric SUV prototypes, where no NVH issues such as rattles or leaks were observed, confirming the efficacy of the modal optimization.
In conclusion, this study demonstrates a systematic approach to modal analysis and optimization of a composite back door for an electric SUV, achieving significant improvements in vibrational performance without compromising lightweight objectives. By employing finite element methods, including modeling in HyperMesh and solving with MSC.Nastran, the first-order bending frequency was successfully elevated from 23.2 Hz to 25.3 Hz through structural enhancements in Scheme 3, while simultaneously reducing mass. This highlights the potential of composite materials and computational design in advancing electric SUV components, offering a pathway to better NVH characteristics and enhanced driving comfort. Future work could explore additional optimization variables, such as material layup sequences or advanced damping techniques, to further refine the back door’s dynamics. Overall, this research provides valuable insights and a reusable framework for the automotive industry, supporting the ongoing evolution of electric SUVs toward greater sustainability and performance. The integration of simulation-driven design not only accelerates development cycles but also ensures that electric SUV back doors meet the rigorous demands of modern vehicles, paving the way for wider adoption of lightweight composites in automotive applications.