Rear Crash Safety

Abstract

In high-speed rear crashes, the seatback needs to be sufficiently strong to manage energy transfer while maintaining the occupant on the seat. Integration of occupant load over seatback displacement or moment over angle change gives the energy transfer capability of a seat. Seatback rotation correlates with occupant kinetic energy transfer, which is determined by the rear crash delta V. The energy transfer is about 2000 J in a 32 kmph rear delta V crash. In low-to-high speed crashes, the head restraint and upper seatback need to reduce relative motion between the head and neck, thus controlling kinematics to prevent “whiplash”. A head restraint height above the head center of gravity and close to the back-of-head provides favorable neck responses. However, the trajectory of the head restraint is forward and downward in a rear crash. This promotes neck extension. A self-aligning head restraint gives a more horizontal direction of head restraint motion and a more upright head and neck orientation. The head restraint moves forward and upward by occupant load on the seatback. This closes the gap behind the head.