Aluminum Subframe Design for Crash Energy Management 2004-01-1775

The engine subframe (cradle) is an important contributor to crash energy management in frontal impact for automotive vehicles. Subframe design can enhance vehicle crash performance through energy management. In addition to energy management targets, the subframe must meet stiffness, durability and other vehicle engineering requirements.

Various subframe concepts are reviewed. Their design intents and vehicle performance are discussed. A development process of an aluminum subframe is then presented which details the subframe design as an energy absorbing component for frontal impacts. The architecture of the subframe is developed based on overall functionality requirements and package constraints. The geometry of the subframe is first designed to accommodate engine mounts and suspension support locations. The subframe member's shape, orientation, and location are then refined to accommodate the subframe-to-body connection requirements.

The safety enhancing structure of the subframe is developed based on the target crash energy. The example design requires that the subframe take an average 8,000 lbs of load. Furthermore, the subframe deformation must not restrict the front rail deformation during frontal crash. Four key elements are identified as energy absorbing components of the subframe. The two pairs of longitudinal members, a connector, and a reinforcing component all collapse to absorb energy. A finite element model is built to simulate a 35 mph rigid barrier frontal impact for design investigations. The analytical results show that a subframe can be designed to meet its crash load carrying requirement and the desired deformation pattern. An optimization process is conducted with selected variables including geometry, thickness and component orientation. The optimization demonstrates that the subframe load capacity can meet a range of energy management targets by modifying key elements. A deformable/detachable mechanism has also been designed to reduce impact force transferred from subframe to body structure.