Influence of child seat payload center of gravity on near-side impact performance

Design features of automotive child restraint systems (CRS) can influence the performance of a child seat in a collision. Various features have been studied regarding side impact performance including the method of anchorage, the side geometry of the CRS, and the padding used for energy absorption. This study investigated the influence of the mass and position of combined CRS and ATD center of gravity (CG), referred to as the payload CG, with regard to the outboard lower anchor and initial contact point of a forward-facing (FF) CRS in near-side impact.

A consistent model of CRS was altered to relocate the CG by rigidly adding a constant mass at different locations on the CRS. Ten deceleration sled tests were conducted using a side impact seat assembly (SISA) attached to the sled at a 10-degree angle, adhering to FMVSS 213a procedures. Lower anchor attachments and top tether were used for all near-side impact tests, and 3-dimensional positions of the CRS CG, CRS initial contact point, and lower anchor were recorded before each test. Data was collected from an instrumented Q3s ATD, as well as video from multiple camera views.

When the CRS weight was increased by 64.4% while keeping a similar CG location, head injury criterion (HIC15) increased by 10.8%. Additionally, for all tests, the most significant correlation found for the HIC was related to an impact axis that is formed between the outboard lower anchor on the seat and the initial contact point on the CRS on the xz-plane. As the payload (CRS and ATD) point mass moment of inertia about the impact axis changed due to the modified CRS, linear regression indicated the HIC15 changed by 37.7 for every 10% change in moment of inertia about the impact axis (p < 0.001). The change in HIC15 corresponded to the peak head y-acceleration, which is tangential to the axis. Other measured data such as chest deflection were investigated, but no other significant correlations were determined.

The HIC had the strongest correlation to the payload mass moment of inertia about the axis formed between the initial contact point on the CRS and outboard lower anchor. Therefore, the most favorable geometry of a CRS for near-side impact would be to design and position the initial impact point close to the combined CRS and ATD CG. By reducing the axis of rotation or mass of the CRS, the payload would have a lower moment of inertia, and the risk of injury to the head could be reduced, all else equal.