The Effects of Recline Angle and Restraint Geometry on Lap Belt-Pelvis Interaction for Above-Normal BMI Motor Vehicle Occupants

The interaction of the three-point seat belt with the occupant, particularly the lap belt with the pelvis, is affected by a multitude of intrinsic and extrinsic factors, including the torso recline angle, lap belt angle, and occupant body mass index (BMI). While field data analyses have shown the strong safety benefit for seat belt use regardless of occupant size or crash direction, the term "submarining" historically has been used to describe a scenario in which the lap belt loads the abdominal soft tissue and organs, superior and posterior to the pelvic bone. While contemporary restraint systems work to effectively address the risk of submarining in occupants properly seated and properly belted, scenarios in which the lap belt may not properly engage the load-bearing pelvis remain. These scenarios, including a reclined torso angle or shallow lap belt angle, require further study. In this research study, eight non-injurious seated belt pull tests were conducted on two constrained whole-body cadavers of above-normal BMI (≥ 25 kg/m2) with controlled variation of torso and lap belt-pelvis angles. Test factors affecting belt engagement with the pelvis were identified for each subject. Belt engagement was largely affected by the initial placement of the lap belt. The initial belt placement was affected by the torso angle which influenced the distribution of the abdominal soft tissue. The belt disengagement thresholds differed between subjects due to the inter-subject differences in soft tissue distribution, which affected the lap belt kinematics relative to the pelvis. In addition to improving the understanding of this particular submarining mechanism, this study provides a dataset for future validation of human body model soft tissue deformation response from lap belt loading.

Effect of various restraint configurations on submarining occurrence across varied seat configurations in autonomous driving system environment

OBJECTIVE

Self-driving technology will bring novelty in vehicle interior design and allow for a wide variety of occupant seating choices. Previous studies have shown that the increased risk of submarining exhibited by reclined occupants cannot be fully mitigated by changes in the seat configuration alone. This study aims to investigate the effects of three restraint countermeasures on cases with marginal submarining events and estimate their effect on submarining risk and injury prediction metrics.

METHODS

Vehicle environment frontal crash Finite Element (FE) simulations were performed with the two simplified Global Human Body Model Consortium (GHBMC) occupant models: small female and midsize male. The baseline occupant restraints consisted of a frontal airbag, a seatback-integrated 3-point belt with a lap belt anchor pre-tensioner, and a retractor-mounted pre-tensioner and load limiter. Based on submarining thresholds identified in previous studies, three baseline configurations were identified for each occupant size. For each baseline case three restraint system modifications were evaluated. The modifications consisted of the introduction of a pelvis restraint cushion airbag (PRC), the use of a knee airbag (KAB) and the modification of the of the passenger airbag location (PAB). Simulations were performed using the USNCAP 56 km/h frontal crash pulse. Occupant kinematic data was extracted from each simulation to investigate how changes in the restraint system configuration affects submarining.

RESULTS

Overall, in only one of the investigated cases did the proposed restraint modification prevent submarining occurrence, however each of the restraint modifications reduced the pelvis excursion over the baseline scenario. The presence of the PRC airbag showed the highest reduction in pelvis forward excursion for the female model. The presence of the KAB and the modified location of the PAB also contributed to reductions in excursion to a smaller degree. For the male surrogate, the KAB showed the highest reduction in pelvis forward excursion. The presence of the PRC led to a reduction in the lumbar spine shear force.

CONCLUSIONS

Submarining may be a major challenge to overcome for reclined occupants in autonomous driving systems. This suggests that there may not be a single generalizable currently-existing countermeasure able to effectively prevent marginal submarining cases in reclined positions.

A numerical investigation of factors affecting lumbar spine injuries in frontal crashes

Recent field data analyses have shown that lumbar spine fractures occurred more frequently in late model vehicles than the early ones in frontal crashes. Therefore, the objective of this study was to investigate risk factors associated with lumbar spine fractures in frontal crashes. Parametric simulations were conducted using a set of validated vehicle driver compartment model, restraint system model, and a HIII mid-size male crash test dummy model. Risk factors considered in the study included occupant seating posture, crash pulse, vehicle pitch angle, seat design, anchor pre-tensioner, dynamic locking tongue, and shoulder belt load limiter. ANOVA and ANCOVA were used to test the statistical significance (p < 0.05). Simulation results showed that all the factors that reduced the risk of submarining increased the lumbar spine forces, indicating a direct conflict between submarining and lumbar spine fractures. Among all the factors selected, seat structure is the most significant factor in determining the lumbar spine force (p < 0.001). Crash pulse severity, time at which the peak crash deceleration reached, and pitch angle are also crucial for lumbar spine force. Specifically, increase in vehicle pitch angle increased lumbar spine force, but reduced injury measures to other body regions; while a crash pulse with early peak produced greater lumbar spine force than that with a late peak. On average, more reclined posture increased the lumbar spine force compared to upright posture, and decreases in the coefficient of friction between the pelvis and the seat cushion reduced the lumbar spine force. However, they are not statistically significant. This study provided better understanding of effects from design countermeasures to reduce occupant lumbar spine injuries in new generation of vehicle models.

Submarining sensitivity across varied anthropometry in an autonomous driving system environment

Objective: Self-driving technology will bring novelty in occupant seating choices and vehicle interior design. Thus, vehicle safety systems may be challenged to protect occupants over a wider range of potential postures and seating choices. This study aims to investigate the effects of occupant size, seat recline, and knee bolster position on submarining risk and injury prediction metrics for reclined occupants in frontal crashes.Methods: Frontal crash finite element (FE) simulations were performed with the 3 simplified Global Human Body Model Consortium (GHBMC) occupant models: small female, midsize male, and large male. Additionally, a detailed GHBMC midsize male model was used to compare with selected simplified cases. For each simulation, parameters including seatback recline angle (0.9°, 10.9°, 20.9°, 30.9°) and knee bolster position relative to the occupant (baseline, close, far, and no knee bolster) were varied. Impacts were simulated with the U.S. New Car Assessment Program 56 km/h frontal crash pulse. Occupant kinematics data were extracted from each simulation in a full-factorial sensitivity study to investigate how changes in anthropometry, seating position, and knee bolster position would affect submarining across all simulated cases.Results: Overall, increasing the occupant-to-knee bolster distance resulted in more submarining cases. The threshold for submarining was also affected by the seat recline angle. The lowest threshold observed occurred with 10.9° of recline with the small female model. Submarining was observed at recline angles at and above 20.9° for the midsize male model and 30° for the large male model. The initial lap belt position, pelvis orientation, and their relationship were good predictors of submarining. Increased lumbar flexion moment was observed with increased seat recline angle as well as occupant-to-knee bolster distance. The detailed GHBMC model was more prone to submarining than the simplified model.Conclusions: Submarining may be a major challenge to overcome for reclined occupants, which may become more prevalent with autonomous driving systems. This study shows that the angle of recline, anthropometric variation, and position of the knee bolster affect the risk of submarining. To our knowledge, this is the first study to computationally evaluate the occupant protection implications of seatback recline for multiple body sizes, postures, and positions relative to the vehicle interior.

Pelvic restraint cushion sled test evaluation of pelvic forward motion

OBJECTIVE

This study was designed to evaluate the performance of a pelvic restraint cushion (PRC), a submarining countermeasure that deploys under the thighs when a crash is detected in order to block the forward motion of the pelvis.

METHODS

Sled tests approximating low- and high-speed frontal impacts were conducted with 4 female postmortem human subjects (PMHS) restrained by a lap and shoulder belt in the right front passenger seat. The subjects were tested with and without a PRC.

RESULTS

The PRC is effective in reducing forward motion of the PMHS pelvis and reduces the risk of injury due to lap belt loading in a high-speed frontal crash.

CONCLUSIONS

Although small sample size limits the utility of the study's findings, the results suggest that the PRC can limit pelvic forward motion and that pelvic injury due to PRC deployment is not likely.

Nature and etiology of hollow-organ abdominal injuries in frontal crashes

Injuries to the hollow organs of the lower digestive system carry substantial risk of complication due to infection and blood loss, and commonly require invasive abdominal surgery to diagnose and treat. The causes of, and risk factors for, lower abdomen injury in automobile collisions are poorly understood. The goal of this study was to investigate the risk factors and potential mechanisms of hollow-organ, lower abdomen injury in belted automobile occupants in frontal collisions. A field survey data analysis was performed to examine the relationship between various occupant and collision factors and the risk of moderate or greater severity injury (i.e., Abbreviated Injury Scale, AIS 2+) to the small intestine, large intestine, or mesentery among belted occupants involved in frontal collisions. Descriptive and comparative risk factor analyses were performed with data originating from that National Automotive Sampling System Crashworthiness Data System (NASS-CDS) over the years 2000-2011. Multivariable logistic regression models were developed to describe the effects of these factors on hollow-organ injury risk. Potential injury mechanisms were further investigated through in-depth examination of select cases exhibiting hollow-organ injuries from the Crash Investigation Research and Engineering Network (CIREN). The inclusion criteria yielded 25,407 individual cases from NASS-CDS, representing a weighted population of 11,373,358 exposed automobile occupants. Within this dataset, 143 cases (weighted frequency: 7962 occupants) exhibited AIS 2+ injury to hollow abdominal organs. Multivariable regression analysis indicated a statistically significant increased risk of moderate or greater severity injuries to the hollow organs of the abdomen with increased in ΔV (odds ratio (OR) 1.07, 95% confidence interval: 1.06-1.09) and age (OR: 1.03, 1.01-1.06). Albeit non-statistically significant, a positive association between BMI and injury risk was observed, especially among obese individuals (OR: 3.55, 0.82-15.2). No association was observed for gender or seated location within the vehicle.

RESULT

from this study indicate that hollow abdominal organ injury is a universal problem in frontal collisions, not confined to a specific gender or seating location. Examination of CIREN cases suggests these types of injuries are associated with direct loading of the lower abdomen by the lap belt, either through poor initial belt positioning or through a "submarining" type of kinematic where the lap belt slips off of the pelvis and loads into the abdomen. Potential countermeasures against hollow-organ abdominal injury should include measures to improve initial lap belt fit, and to retain engagement of the lap belt on the pelvis throughout the collision event.