Function-Oriented Sub-Frame Design for a Hydraulic Hybrid Vehicle

HLA Sub-frame Design Developed at MKP with the Installed Vehicle inside TACOM

Project HAMMER (Hydraulic hybrids, Advanced Materials, & Multi-fuel Engine Research) is funded by the U.S. Army TACOM to promote a hydraulic hybrid vehicle technology for both military and commercial trucks that will become more environmentally compliant and fuel efficient. 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, which is stored in hydraulic oil and nitrogen gas inside the high pressure accumulator. When the vehicle is accelerating, the highly pressured oil flows through the hydraulic p/m and the stored energy is released to propel the vehicle.

The key component in this new system is a HLA (Hydraulic Launch Assist) unit, which employs an advanced hydraulic hybrid powertrain system. The HLA system weights over 600 lbs, and to fit it into a traditionally designed vehicle, as well as to fit multiple candidate platforms, the design of a subframe that can mount the HLA to the vehicles is a critical task. The previous subframe design of the HLA system failed during a road test, and thus there is an urgent need to develop a new design, which is not only more durable, but also has function to isolate the vibration and noise of the HLA system. Light weight is another requirement for the new subframe, and the new design effort is expected to support reducing the weight of HLA itself. Furthermore, the subframe design needs to be flexible, so it can fit the HLA unit into different platforms. The design target also includes the associated mounting system and bushings.

The overall objective of this research is to design an optimum and lightweight subframe system for the HLA unit in support of the HAMMER program. The specific objectives of the subframe design include maximizing vibration isolation between the vehicle frame and subframe and minimizing the weight of the subframe subject to the durability requirements, desired vibration characteristics, cost, and manufacturability. The HLA unit is still under seperate development, the design concept has varied, so, the subframe design needs to catch up to it. Therefore, an effective and efficient design process is necessary for laying out an optimum design. A function-oriented design process based on advanced topology optimization techniques is employed in this research. The resulting design of the sub-frame greatly improves the performances of the hydraulic hybrid unit, which leads to a more marketable vehicle system.