Sub-Frame Design for a Hydraulic Hybrid Vehicle System

Hybrid vehicles are gaining increasing popularity in recent years, and there are three major types of hybrid systems, hybrid hydraulic, hybrid electric, and hybrid fuel cell. The hydraulic system offers great advantages for vehicles operating in stop-and-go conditions because the reversible hydraulic pump/motor can capture large amounts of energy when the brakes are applied, and this energy is released through the hydraulic pump/motor to propel the vehicle. The key component in this new system is a HLA (Hydraulic Launch Assist) unit, which employs an advanced hydraulic hybrid power train system. Technical challenges with hydraulic hybrids include packaging and noise issues. HLA is an over 600 lbs system, and to fit it into a traditional designed vehicle, as well as to fit possibly multiple candidate platforms, the design of a sub-frame that can mount the HLA to the vehicles is a critical task. Because HLA system development is an on-going work, different structural problems emerge during this process. Therefore, an efficient design system is necessary to address the problems in the up-front design stage. Function-Oriented Material Design (FOMD) with special topology optimization techniques, such as multi-domain multi-step topology optimization, is a tool suitable for this task. The theoretical background is described and sub-frame design process is summarized in this paper. The effectiveness of the design system is demonstrated through design examples. The design method and procedure proposed in this paper is applicable to other vehicle structural design problems, which will reduce the design cycle and achieve the required functionalities in an efficient way.