Redesign of a 2005 Chevy Equinox Rear Cradle for the Implementation of a Hybrid Electric Drive

The Mississippi State Challenge X team has built a new rear cradle for its 2005 Chevy Equinox hybrid, which allows for the integration of a Ballard electric drive system. The OEM cradle would have required extensive modification for the installation of the Ballard unit. The new cradle will save space by utilizing smaller members with thicker walls, thereby permitting more flexibility in mounting the drive.

The team developed a working model of the MSU cradle that serves the duties of the existing cradle and allows the Ballard drive to be installed. Analytical calculations were performed to determine the loads experienced by the cradle during on-road service. A stress analysis was then performed using these loading criteria.

The MSU team determined that mechanical testing would be the fastest way to analyze the stiffness of the original part. Two mechanical tests were performed to determine the part's stiffness. In the first case, a horizontal load was applied to one of the suspension mounting flanges. The displacements and loads were recorded and used in a finite element analysis (FEA) of the new cradle. The second test was to measure the bending stiffness of the main structural members in the vertical direction.

The MSU cradle maintains the stock cradle's bending stiffness and weighs essentially the same as the stock cradle while providing adequate room for the installation of the Ballard electric drive system.