Optimizing frontal impact occupant protection systems for passengers seated in wheelchairs

OBJECTIVE

The advent of automated vehicles (AVs) provides an opportunity to design integrated wheelchair seating stations that provide an equivalent level of safety for occupants using wheelchairs as those using vehicle seating. This study designed a frontal occupant protection system for an integrated second-row wheelchair seating station that includes optimized airbags and seatbelt systems.

METHODS

MADYMO models were used to optimize belt geometry for a midsized male ATD seated in a surrogate wheelchair fixture, with and without inclusion of a Self Conforming Rearseat Air Bag (SCaRAB). Sled tests were performed to confirm the benefits of airbag use and optimized belt geometry. Additional modeling was performed with commercial manual and power wheelchairs, to identify the effects of wheelchair design and forward clear space on occupant kinematics and injury measures. Additional sled tests were performed with manual and power wheelchairs to demonstrate effectiveness of the restraint system with commercial products.

RESULTS

Simulations and tests both showed improved kinematics using an optimized seatbelt system geometry compared to a commonly used suboptimal D-ring location that places the shoulder belt at a more outboard location. Use of the SCaRAB helped compensate for suboptimal geometry. Results include specific recommendations for belt geometry relative to the wheelchair seating station and airbag parameters suitable for protecting occupants seated in wheelchairs. Restraint systems initially optimized using the surrogate wheelchair also performed well with the two commercial wheelchairs. The clear space required for maneuvering a wheelchair will likely prevent injurious head contact in frontal crashes.

CONCLUSIONS

This study is the first to design a frontal optimal occupant protection system for an integrated second-row wheelchair seating station, demonstrating that it should be feasible once integrated wheelchair seating stations are included in AVs.

Dynamic metrics to differentiate booster performance

OBJECTIVE

The purpose of this research was to explore candidate booster performance metrics that may have the potential to identify less effective booster systems, because current FMVSS No. 213 booster performance requirements can be met without a booster.

METHODS

To provide a more realistic test environment, dynamic testing was performed using a surrogate seat belt retractor on the most recent preliminary design update proposed for the FMVSS No. 213 seat assembly. Given that field data show that belt-positioning boosters are effective at reducing injury risk, potential testing measures were assessed relative to data collected for the no-booster condition. Eleven booster products were evaluated, as well as the no-booster condition, with 6 tests performed using the Hybrid III 10-year-old and 33 tests run with the Hybrid III 6-year-old.

RESULTS

Possible metrics associated with good anthropomorphic test device (ATD) kinematics (no submarining or rollout) were the difference between knee and head excursion, maximum torso angle, lumbar spine Moment Z, and lumbar spine Force Y.

CONCLUSIONS

When testing boosters under more realistic dynamic conditions, the proposed metrics would allow better discernment of less effective boosters, because they differentiate performance relative to the no-booster condition.

Effects of child restraint misuse on dynamic performance

Objective: Estimates of child restraint misuse rates in the United States range from 49% to 95%, but not all misuse modes have similar consequences in terms of restraint effectiveness. A series of laboratory sled tests was conducted to determine the effects of common misuses and combinations of misuses, including loose harness, loose installation, incorrect installation angle, incorrect belt path, loose/no tether, and incorrect harness clip usage.Methods: Three commercial convertible child restraint models were loaded with the Hybrid III 3-year-old anthropomorphic test device (ATD) and secured by either LATCH or seat belt on a modified FMVSS No. 213 bench. Tests were conducted in forward-facing (FF) and rear-facing (RF) modes. The response variables included ATD accelerations, excursions, and restraint kinematics. Belt/LATCH loads, tether loads, ATD kinematics, and restraint structural response data were also documented. A fractional factorial test design on 8 factors was used to define an initial series of 32 tests. The first series also included 4 tests of correct CRS, 2 forward facing and 2 rearward facing. The analysis of those data determined the selection of conditions for the remaining 20 tests to focus on factors and interactions of high interest and significance.Results: In the RF condition, misrouting the LATCH belt or seat belt through the incorrect belt path was the only misuse that significantly affected outcomes of interest and was associated with high levels of undesirable CRS rotation. In FF tests, loose installation and tether misuse had large adverse effects on 3 of 4 key response variables.Conclusion: The study provides strong evidence for prioritizing tight restraint installation and proper tether use for FF restraints. In particular, use of the tether helped offset the adverse effects of loose installation or loose harness. Because the results show that performance of a RF child restraint system (CRS) installation is less affected by user error, they also provide support for extended RF restraint use. In addition, packaging convertible child restraints with the LATCH belt routed through the RF belt path could help prevent the most consequential RF CRS misuse.

Factors affecting tether use and correct use in child restraint installations

INTRODUCTION

Field studies show that top tethers go unused in half of forward-facing child restraint installations.

METHOD

In this study, parent volunteers were asked to use the Lower Anchors and Tethers for Children (LATCH) to install child restraints in several vehicles to identify tether anchor characteristics that are associated with tether use. Thirty-seven volunteers were assigned to four groups. Each group tested two forward-facing child restraints in four of 16 vehicle models. Logistic regression models were used to identify predictors of tether use and correct use.

RESULTS

Subjects used the tether in 89% of the 294 forward-facing child restraint installations and attached the tether correctly in 57% of the installations. Tethers were more likely to be used when the anchor was located on the rear deck as typically found in sedans compared with the seatback, floor, or roof. Tethers were less likely to be attached correctly when there was potentially confusing hardware present. No vehicle tether hardware characteristics or vehicle manual directions were associated specifically with correct tether routing and head restraint position.

CONCLUSION

This study provides laboratory evidence that specific vehicle features are associated with tether use and correct use.

PRACTICAL APPLICATIONS

Modifications to vehicles that make tether anchors easier to find and identify likely will result in increases in tether use and correct use.

Development and testing of a more realistic pelvis for the Hybrid III 6-year-old ATD

OBJECTIVE

Design and test a new pelvis for the Hybrid III 6-year-old (6YO) anthropometric test device (ATD) with a more humanlike bone structure, flesh contour, and flesh stiffness intended to provide more realistic interaction with belt restraints.

METHODS

Target geometry for the new pelvis bone was based on a 3D model of the skeletal pelvis derived from statistical analysis of pediatric computed tomography (CT) scans. The current pelvis bone was reshaped to better match the target geometry, with a particular emphasis on the contour in the areas of belt interaction. The prominence representing the anterior-superior iliac spine (ASIS) was lowered by 15 mm. The pelvis flesh was molded using softer vinyl while maintaining a 10-mm flesh margin over the ASIS. A series of 20 sled tests was conducted to compare the performance of the modified pelvis with the current Hybrid III pelvis.

RESULTS

In a series of sled tests using a range of belt anchorage locations, a dummy equipped with the new pelvis did not submarine in conditions where the lap belt was positioned below the ASIS. Tests run with the lap belt initially positioned over the ASIS resulted in submarining, unlike tests performed with the standard dummy pelvis.

CONCLUSIONS

The new pelvis for the 6YO Hybrid III ATD better represents the skeletal and flesh geometry of similar-sized children. The ATD equipped with the new pelvis is more sensitive to lap belt geometry than the standard ATD. The modified ATD may provide an improved assessment of booster seats and belt restraints intended for child occupants.