1. Introduction
Lightweight is an important way to achieve energy saving and emission reduction [
1,
2]. Whether traditional or new energy vehicles, reducing the vehicle weight has the advantages of reducing energy consumption, improving power performance and braking performance [
3,
4]. In the “Made in China 2025” strategy, lightweight technology is listed as one of the core technologies to achieve the development goals of energy saving and new energy vehicles.
Scholars have carried out many related researches on automobile lightweight, and the main contents are how to realize automobile lightweight by optimizing structural design, applying lightweight materials and adopting advanced manufacturing processes [
5,
6]. In terms of lightweight design method, Paz et al. [
7] improved the energy absorption characteristics of automobile energy absorption device and reduced the mass by using surrogate model technology and multi-objective genetic algorithm. Velea et al. [
8] carried out multi-objective optimization for the composite body of electric vehicle considering the weight, cost, and stiffness. Duan et al. [
9] used multi-objective particle swarm optimization algorithm for lightweight design of body-in-white structure to meet the reliability requirements. Li et al. [
10] improved the crashworthiness of the vehicle under low-speed collision by optimizing the front structure of the vehicle body. Wang et al. [
11] carried out lightweight multi-objective optimization design of bus body frame using modular local topology optimization design method. The above research mainly focuses on the lightweight design of automobile body structure. The lightweight of suspension structure is an important part of vehicle lightweight. It is necessary to study the lightweight design method of suspension structure.
Recently, the parametric modeling method based on mesh morphing technology is widely used in the field of automobile lightweight. Sharma [
12] used mesh morphing technology to establish an interdisciplinary parametric model in the process of vehicle structure optimization. Wang et al. [
13] combined with mesh deformation technology and optimization method for lightweight design of car subframe. Lian [
14] used parameterized mesh deformation function to quickly generate finite element models of buses with different sizes for building approximate models. Fang et al. [
15] performed multi-objective shape optimization of body-in-white frame beam based on mesh morphing technology to reduce weight. Suspension structure usually has a relatively complex structure, and its lightweight design is only considering the thickness of the plate, which leads to the optimization space is limited, and the lightweight effect is not obvious. Compared with size optimization, the parametric model based on mesh morphing technology is used for shape optimization [
16], which can fully exploit the weight reduction potential of suspension structure and make its lightweight effect more significant.
The lightweight design of suspension structure will change its structural performance such as stiffness and mode, which will cause the change of suspension performance, and then affects the vehicle performance such as ride comfort and handling stability [
17]. At the same time, there is a coupling relationship between the performance of the front and rear suspensions. The lightweight design of the front suspension structure or the rear suspension structure alone, while ignoring the synergy between them, often reduces the engineering applicability of the lightweight scheme. Therefore, the lightweight design of suspension structure is a complex system optimization problem. In the design process, it is necessary to consider not only its own structural performance index, but also the coupling relationship between the front and rear suspension structural parameters to ensure that the vehicle performance such as ride comfort and handling stability meets the requirements. In addition, the suspension structure is an important bearing part of the chassis, which needs to bear the force and torque from the three directions between the road and the body during the vehicle driving. The load condition is complex, especially the lightweight design will usually improve the structural stress level, which is easy to cause structural fatigue failure [
18]. Therefore, the fatigue resistance is also one of the important evaluation indexes to be considered in the lightweight design of suspension structure.
The lightweight design of suspension components has a negative effect on vehicle dynamic performance such as ride comfort and handling stability. Also, there is a synergy between front and rear suspensions, which affects the engineering applicability of lightweight scheme of suspension component. Hence, it is necessary to conducted the lightweight design of suspension components while considering their structural performance and the vehicle dynamic performance. In this paper, the lower control arm of the McPherson front suspension and the torsion beam of the rear suspension are taken as the research objects. The parametric modeling of the control arm and the torsion beam is carried out based on the mesh morphing technology. The shape parameters and thickness reflecting the structural characteristics are selected as the design variables, and the rigid–flexible coupling model of the vehicle considering the flexibility of the control arm and the torsion beam is established. On this basis, the structural performance such as fatigue life, stiffness and modal frequency, and the vehicle performance such as ride comfort and handling stability are comprehensively considered. Combined with the Kriging surrogate model and the NSGA-II algorithm, the size optimization and shape optimization of the control arm and the torsion beam are carried out simultaneously, for realizing the lightweight design of suspension components.
The rest of this paper is structured as follows: The parametric models of control arm and torsion beam are presented in
Section 2. In
Section 3, the vehicle rigid–flexible coupling model is established. In
Section 4, the lightweight design of control arm and torsion beam is performed based on NSGA-II algorithm coupling with surrogate model. The multi-objective optimization results are discussed and analyzed in
Section 5. Finally, the main conclusions are outlined in
Section 6.
6. Conclusions
In this paper, the lightweight design method of suspension components is study based on multi-objective optimization algorithm and surrogate model by considering structural performance and vehicle dynamics. The parameterized models of the control arm and torsion beam are first developed to define the design variables based on mesh morphing technology. The lightweight design problem is formulated with three conflicting objectives, including total weight of control arm and torsion beam, total weighted root mean square of seat rail acceleration for evaluating ride comfort, and maximum vehicle roll angle for handling stability evaluation. The structural performance, such as fatigue life, stiffness, and modal frequency, are considered as constraints as well. Subsequently, the Kriging models are constructed to describe the relations between design variables and responses. The NSGA-II algorithm is then adopted to identify the Pareto front. The lightweight design scheme is determined from these non-dominated solutions by balancing the weight and vehicle dynamic performance.
By comparing optimized and original design scheme, it is concluded that the lightweight design of the control arm and torsion beam not only achieves a remarkable mass reduction, but also gets some improvement for structural performance and vehicle dynamic performance. The proposed lightweight method is proved to be feasible and effective for simultaneous lightweight design of front and rear suspension components.