Optimized Ride-Down Rate Control in Frontal Impact and its Application in the Energy Management of Occupant Restraint System 2013-01-0760

This paper presents an analytic approach to determining the optimized ride-down rate-the relative amount of occupant kinetic energy dissipated in vehicle structure deformation, and attempts to address the question of how the desired ride-down rate could be realized in vehicle design. In this paper the ride-down rate is divided by a critical ride-down rate value into two areas: a positive-effect-area where an increase of ride-down rate will lead to a decrease in the occupant injury level, and a negative-effect-area where an increase in ride-down rate could lead to an increase in the occupant injury level. The critical ride-down rate is found to occur at around 50% for a sedan class vehicle frontal crash into a rigid barrier at 56 km/h of NCAP test setup. The critical ride-down rate can also be estimated with various constraints such as occupant injury levels, vehicle categories and crash modes. Ride-down rate measurements from NCAP tests showed satisfactory agreement with the analytical calculation results from the ride-down rate models.

This paper also presents a ride-down rate control approach in terms of coupling design between the occupant restraint system and dynamic structural behavior. Impact event timing control and occupant travel space compatibility with respect to the compartment are found to be critical in ride-down rate control. A theoretical analysis on the relationship between the ride-down rate, impact timing, and the occupant relative displacement/structure crush ratio is presented and compared with the measurements from NCAP tests. Occupant relative displacement with respect to the vehicle is treated as an engineering variable that could control the ride-down rate in a vehicle safety design.

Setting the capacity levels for each sub-restraint system in the beginning of system integration is a critical starting step, because it would reduce costly late engineering changes. An approach to energy management of an occupant restraint system is finally given based on the optimized ride-down rate control concept. Optimized ride-down rate makes it possible to configure a desired occupant energy curve by a trapezoid in displacement domain, which could be used to distribute the occupant kinetic energy into sub-restraint systems such as airbag, safety belt and steering column.

The interactions between safely belt, airbag and steering wheel have been discussed in publications. This paper isolates each sub-system from the complex interaction by using the trapezoid analysis method in the displacement domain, which sets a series of minimum performance criterion for each sub-restraint system. This procedure of breaking down the performance criterion for sub-restraint systems is finally validated by inputting a set of sub-restraint system parameters into a numerical model. The dynamic response from this numerical model correlated very well with the desired trapezoid energy curve in the displacement domain, from which the input parameters were generated.