Top tether effectiveness during side impacts

ABSTRACT

Objective: Few studies have looked at the effectiveness of the top tether during side impacts. In these studies, limited anthropomorphic test device (ATD) data were collected and/or few side impact scenarios were observed. The goal of this study was to further understand the effects of the top tether on ATD responses and child restraint system (CRS) kinematics during various side impact conditions.

Methods: A series of high-speed near-side and far-side sled tests were performed using the FMVSS213 side impact sled buck and Q3s ATD. Tests were performed at both 10° and 30° impacts with respect to the pure lateral direction. Two child restraints, CRS A and CRS B, were attached to the bench using flexible lower anchors. Each test scenario was performed with the presence and absence of a top tether. Instrumentation recorded Q3s responses and CRS kinematics, and the identical test scenarios with and without a top tether attachment were compared.

Results: For the far-side lateral (10°) and oblique (30°) impacts, top tether attachment increased resultant head accelerations by 8–38% and head injury criterion (HIC₁₅) values by 20–140%. However, the top tether was effective in reducing lateral head excursion by 5–25%. For near-side impacts, the top tether resulted in less than 10% increases in both resultant head acceleration and HIC₁₅ in the lateral impact direction. For near-side oblique impacts, the top tether increased HIC₁₅ by 17.3% for CRS A and decreased it by 19.5% for CRS B. However, the injury values determined from both impact conditions were below current injury assessment reference values (IARVs). Additionally, the top tether proved beneficial in preventing forward and lateral CRS rotations.

Conclusions: The results show that the effects of the top tether on Q3s responses were dependent on impact type, impact angle, and CRS. Tether attachments that increased head accelerations and HIC₁₅ values were generally counterbalanced by a reduction in head excursion and CRS rotation compared to nontethered scenarios.

KEYWORDS:

• LATCH
• top tether
• child safety
• child restraint system
• side impact

Acknowledgments

The authors would like to acknowledge Tom Batalaris, Jeremy Belzyt, Jon Rieman, and Charlie Hall from Evenflo (Piqua, Ohio) for supporting the sled tests.

Funding

The authors acknowledge the National Science Foundation (NSF) Center for Child Injury Prevention Studies at the Children's Hospital of Philadelphia (CHOP) and the Ohio State University (OSU) for sponsoring this study and its Industry Advisory Board (IAB) members for their support, valuable input, and advice. The views presented are those of the authors and not necessarily the views of CHOP, OSU, the NSF, or the IAB members.