Virginia Tech Doubles the Strength of Its Rear Subframe with Redesign

The Hybrid Electric Vehicle Team of Virginia Tech (HEVT) has spent nearly two years redesigning its rear subframe to meet EcoCAR 2 requirements for stress and strength factors of safety.

“The redesigned rear subframe is important for a couple of reasons,” said HEVT mechanical subteam member Chris Eaton. “First, it contributes to the overall safety of our vehicle by providing structural strength and stability. Second, the redesigned rear subframe allows us to completely package our rear powertrain which is required for all modes of operation.”

While the redesigned rear subframe is just as stiff as the previous model, it is twice as strong. To achieve this, Virginia Tech’s mechanical subteam had to first determine which locations on the subframe needed the most support and where they needed to add reinforcements. Next, they had to identify which shape or geography would best fit the design criteria. Finally, they performed the required finite element analysis (FEA) to accurately represent the stress and displacement generated within the subframe while under different types of loading.

The finished product includes two major modifications from the original. First, HEVT changed the angles at which the front cross member approaches the rest of the subframe from 90° to roughly 140°. This reduces stress. Second, they added a new arching cross-member, which will assist with load distribution across the rear portion of the subframe.

CAD models of three stages of HEVT’s redesign process

CAD models of three stages of HEVT’s redesign process

In addition to successfully developing a redesigned rear subframe that meets both competition and team (HEVT) requirements, this project also provided a great chance to learn.

“I have learned an immeasurable amount about the modeling, drafting, and simulation aspects of computer-aided design (CAD),” Eaton said.

The team also learned about how a product moves through the design, fabrication and installation phases. While working on the subframe, we reached out to professional engineers at companies like General Motors and Siemens, which was a great opportunity to learn and network.

With the redesigned rear subframe complete, HEVT can now focus on testing the exhaust system to ensure that it does not leak. We will also be working on the refinement and installation of components associated with our fuel system.

“I look forward to seeing how the rest of the semester unfolds and how we favor during competition this summer. I believe that we can place well in competition if we finish out the rest of the semester on a strong note,” Eaton said.