Study of Second Seat Row Occupant Protection in Frontal Vehicle Crashes and Potential Restraint System Countermeasures

Legal requirements regarding the qualification of the second seat row restraint system with anthropomorphic test devices (ATDs) currently do not exist. Consumer tests with respect to mass production rear occupant protection systems are already being planned or even executed and the results are or will be publicly available. However, there are various factors that make it difficult to apply the strategies applied for first row occupants to second row occupants. Also, there are differences regarding seat deformation and applied decelerations relative to the first row occupants. The purpose of this study is to evaluate the effectiveness of various restraint system components for second seat row occupants. Sled tests with different occupant sizes have been conducted and analyzed in the second seat row. Based on these tests, a numerical simulation model has been built and correlated for various crash modes. Investigations were conducted that evaluate the relevant restraint parameters and their impact on the occupant protection performance for second seat row occupants. Restraint components have been modified in order to determine their potential to enable a premium rating under the current consumer test protocols for second row occupants. A reduction of the external loads applied to the ATD due to the use of pyrotechnic seat belt pretensioners and seat belt load limiters has been shown. Low force levels result in increased displacement of the occupant’s head and thorax and therefore increases the risk of occupant contact to the vehicle interior components. The potential of controlling the head kinematics with the seat belt alone without the addition of other restraint components is limited. A conventional 3-point seat belt seems to be insufficient to secure premium ratings for future consumer test programs. Additional inflatable devices like an airbelt allow a further reduction of the occupant loads with comparable or even reduced occupant displacement. Adaptive seat belt components with selectable force levels are recommended since this technology allows a reasonable trade-off between reduced occupant loads and controlled occupant displacement for various occupant sizes. Additional influencing factors for the occupant loads have been identified, including: the mechanical and geometrical properties of the seat ramp, and the timing and intensity of the vehicle pitch.