Approach for the development of suspensions with integrated electric motors

Abstract

Conceptual design is an innovative and strategic phase in the process of product development. In this phase the concept generation and decision-making are critical to the following product development. However, it is a challenge to generate the realizable design concepts and then make a right decision because of involved multidisciplinary design and insufficient information. Lightweight design is a non-negligible and high priority subject in the concept design phase of electric vehicles. Combining the drive unit into suspension links is an effective engineering solution to achieve system lightweight while realizing the low increase of the unsprung mass. However, these questions arise from this idea: how the suspension concepts with integrated electric motors can be systematically generated and evaluated with consideration of complex functions, multiple design parameters and their intricate relationships? How an axle structure can be designed to be lightweight and suit this combined concept? How the ride dynamics of the vehicle with this suspension is evaluated? This thesis presents a design methodology for the development of suspension concepts in which links are combined with electric motors. Firstly, a new approach for concept design to integrating the functions based on the Axiomatic Design is proposed. In this approach, the integration process is formulaically and explicitly expressed by matrix equations. The system functions, corresponding parameters and their relationships can be investigated in the design matrices. This approach is then applied to the design of suspension concepts which integrate the functions of electric motors. The generated concepts are evaluated and selected by comparing their design matrices according to the Axioms introduced in Axiomatic Design. Subsequently, a reference suspension is tested and the parameters are used as the benchmark for the development of the suspension concept. The design matrix of the suspension concept is further to guide the subsequent engineering development. The design variables in the matrix are determined in the order in which the mathematical matrix equations are solved. To further reduce the system mass, a topological design approach considering the suspension kinematics and compliance is proposed for the design of suspension structure. On the basis of the structure topology, a lightweight linkage consisting of steel tubes with different thickness is achieved. The characteristics of the suspension concept are compared with the reference suspension. In order to investigate the vertical and roll dynamics of the concept suspension, an analytical model for the rear-axle vehicle dynamics and a road model for double lane irregularities in accordance with the ISO road standards are developed. These models can simulate the ride and roll dynamics of the target vehicle with the concept rear-axle on the ISO standard road surface. The ride dynamics with the new suspension is compared with the reference suspension.