Multi-objective Collaborative Optimization for the Lightweight Design of an Electric Bus Body Frame
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Multi‑objective Collaborative Optimization for the Lightweight Design of an Electric Bus Body Frame Dengfeng Wang1 · Chong Xie1 · Yuchang Liu2 · Wenchao Xu1 · Qi Chen1 Received: 25 February 2020 / Accepted: 28 June 2020 © China Society of Automotive Engineers (China SAE) 2020
Abstract To analyze the rollover safety, finite element models were established for the electric bus body frame, rollover simulation platform, living space, and bus rollover. The strength and stiffness of the body frame were calculated under four typical working conditions considering the main low-order elastic modal characteristics. The results indicate that the initial body frame of the electric bus satisfies the required structural strength, stiffness, modes, and rollover safety, and it has great potential for lightweight design. Sensitivity and structural contribution analyses were performed to determine the design variables for lightweight optimization of the body frame, and a mathematical model was established for multi-objective collaborative optimization design of the electric bus. Then, the radial basis function neural network was used to approximate the optimization model. Besides, the accuracy of the approximate model was verified, and the non-dominated sorting genetic algorithm II was employed to determine solutions for the lightweight optimization. Compared with the initial model, the mass of the optimized model is reduced by 240 kg (9.0%) without any changes in the materials of the body frame. Keywords Electric bus · Body frame · Lightweight optimization · Structural contribution analysis · Multi-objective collaborative optimization Abbreviations NSGA-II Non-dominated sorting genetic algorithm II RBF Radial basis function
design can greatly improve the overall vehicle performance [1]. Research on the lightweight design of the bus body frame can be summarized as follows:
1 Introduction
1. Finite element models (FEMs) have been established for the bus body frame under typical working conditions to analyze the basic static and dynamic performances and evaluate whether the structure presents the required strength, stiffness, and modal characteristics [2, 3]. 2. The body frame has been optimized for a lightweight design based on the main low-order elastic modal frequencies and its strength and stiffness under typical working conditions without changes in the materials [4–6]. 3. FEMs have been established for the rollover to improve safety, and corresponding structural improvement measures have been proposed after dynamic analysis [7, 8]. 4. Single- or multi-objective optimization methods have been used to reduce the weight while ensuring that the required strength, stiffness, modal frequency, and rollover safety of the body frame are satisfied [9–15].
Reducing weight is an important technical path for lowering energy consumption, material consumption, and emissions in the automotive industry. For an electric bus, the power battery pack increases the total mass by 2–3 tons compared with a bus using conventional fuel. This great
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