Knee Airbag Research Articles

Optimization on parameters of knee airbag considering driver’s instinctive response

Optimization on parameters of knee airbag considering driver’s instinctive response

Injury effects of knee airbags on Chinese human dummy

Two kinds of knee airbags and dummy crash simulation models are established, and the accuracy of the models is verified by comparing the knee module impact test data and CAE simulation data. A knee airbag and dummy crash simulation system is established, and the frontal collision finite element simulation of the Chinese 50th percentile dummy is carried out under the three conditions of no knee airbag, bottom-mounted knee airbag, and rear-mounted knee airbag. According to the regulations of China-New Car Assessment Program (CNCAP), the injury data of major body parts such as the head, chest, femur, and legs are compared and analyzed, and the differences in damage to the dummy caused by the bottom-mounted knee airbag, the non-knee airbag and the rear-mounted knee airbag are focused on. Conclusion: Compared with the HIII dummy with knee airbag, the chest compression and tibia compression force of the Chinese dummy with knee airbag are larger, and the compression force of femur is smaller; compared with the condition without knee airbag, the value of head acceleration, tibial index, chest deformation, etc of Chinese dummy can be reduced with knee airbag, but the tibial axial force and knee side displacement have increased; compared with the condition of the rear-mounted knee airbag, the bottom-mounted knee airbag has better protection performance for the dummy’s head, chest, upper leg, and lower leg, but the knee side displacement of bottom-mounted knee airbag is greater, and the axial compression of the tibia is greater. This paper can provide a theoretical basis for the design of knee airbag in the Chinese market and the development of Chinese human dummy.

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.

Restraint systems considering occupant diversity and pre-crash posture

Objective Use volunteer data and parametric finite element (FE) human body models to investigate how restraint systems can be designed to adapt to a diverse population and pre-crash posture changes induced by active safety features. Methods Four FE human models were generated by morphing the midsize male GHBMC simplified model into geometries representing a midsize male, midsize female, short obese female (BMI 40 kg/m2), and large obese male (BMI 40 kg/m2) based on statistical skeleton and body shape geometry models. Each human model was positioned in a generic vehicle driver environment using two occupant pre-crash postures based on volunteer test results including one resulting from 1-g abrupt braking events. Improved restraint designs were manually developed for each occupant model in a 56 km/h frontal crash condition by adding a knee airbag, adjusting the shoulder belt load limit, steering column force, and driver airbag properties (tethers, inflation, and vent size). The improved designs were then tested at both pre-crash postures. Injury risks for the head, neck, chest, and lower extremities were analyzed. Results Human size and shape dominated the occupant injury measures, while the pre-crash-braking induced posture had minimal effects. Some of the safety concerns observed for large occupants include head strike-through the airbag and a conflict between head and chest injuries, which were mitigated by a stiffer restraint system with properly-tuned driver airbag. Chest injuries were a prominent safety concern for female occupants, mitigated by a softer seatbelt and smaller airbag size near the chest. Obese occupants exhibited a higher likelihood of lower extremity injuries indicating a need for a knee airbag. A diverse set of improved restraint designs were effective in lowering injury risks, indicating that restraint adaptability is necessary for accounting for occupant diversity. Conclusions This study investigated the effects of occupant size and shape variability, posture, and restraint design on injury risk for high-speed frontal crashes. More forward initial postures due to active safety features may decrease head, neck, and lower extremity injury risk, but may also increase chest injury risk. Safety concerns observed for large occupants include head strike-through and a conflict between head and chest injuries. Obese occupants had higher knee-thigh-hip injury risk. New restraints that adapt to occupant size and body shape may improve crash safety for all occupants. Further investigation is needed to confirm and extend the findings of this study.

Active muscle response contributes to increased injury risk of lower extremity in occupant–knee airbag interaction

ABSTRACTObjective: Recent field data analysis has demonstrated that knee airbags (KABs) can reduce occupant femur and pelvis injuries but may be insufficient to decrease leg injuries in motor vehicle crashes. An enhanced understanding of the associated injury mechanisms requires accurate assessment of physiological-based occupant parameters, some of which are difficult or impossible to obtain from experiments. This study sought to explore how active muscle response can influence the injury risk of lower extremities during KAB deployment using computational biomechanical analysis.Methods: A full-factorial matrix, consisting of 48 finite element simulations of a 50th percentile occupant human model in a simplified vehicle interior, was designed. The matrix included 32 new cases in combination with 16 previously reported cases. The following influencing factors were taken into account: muscle activation, KAB use, KAB design, pre-impact seating position, and crash mode. Responses of 32 lower extremity muscles during emergency braking were replicated using one-dimensional elements of a Hill-type constitutive model, with the activation level determined from inverse dynamics and validated by existing volunteer tests. Dynamics of unfolding and inflating of the KABs were represented using the state-of-the-art corpuscular particle method. Abbreviated Injury Scale (AIS) 2+ injury risks of the knee–thigh–hip (KTH) complex and the tibia were assessed using axial force and resultant bending moments. With all simulation cases being taken together, a general linear model was used to assess factor significance (P <.05).Results: As estimated by the regression model across all simulation cases, use of KABs significantly reduced axial femur forces by 4.74 ± 0.43 kN and AIS 2+ injury risk of KTH by 47 ± 6% (P <.05) but did not provide substantial change to injury risk of leg fractures. Muscle activation significantly increased axial force and bending moment of the femur (3.87 ± 0.38 kN and 64.3 ± 5.9 Nm), the tibia (1.49 ± 0.12 kN and 43.0 ± 6.4 Nm), and the resultant probability of AIS 2+ tibia injuries by 36 ± 6% regardless of KAB use and crash scenario. Specifically, when counting on a relative scale, muscle activation exhibited more prominent elevation of injury risk for in-position occupants than out-of-position occupants. In a representative crash scenario—that is, using a bottom-deployed KAB in a nearside oblique impact—muscle bracing of the right leg may lead to 2.6 times higher tibia fracture risk than being relaxed for an out-of-position occupant and 5.4 times higher for an in-position occupant.Discussion and Conclusions: The mechanism of higher leg injuries in the presence of KAB deployment in real-world crashes can be interpreted by the increased effective body mass, axial compression along the shafts of long bones, and altered pre-impact posture due to muscle contraction. The present analysis suggests that active muscle response can increase the risk of lower extremity injury during occupant–KAB interaction. This study demonstrated the feasibility of advanced human models to investigate the influence of physiologically based parameters on injury outcomes evidenced in field study and insight from computational examination on human variability for development of future restraint systems. Future efforts are recommended on realistic vehicle and restraint environment and advanced modeling strategies toward a full understanding of KAB efficacy.

Computational investigation of the effects of knee airbag design on the interaction with occupant lower extremity in frontal and oblique impacts

ABSTRACTObjective: The lower extremity of the occupant represents the most frequently injured body region in motor vehicle crashes. Knee airbags (KABs) have been implemented as a potential countermeasure to reduce lower extremity injuries. Despite the increasing prevalence of KABs in vehicles, the biomechanical interaction of the human lower extremity with the KAB has not been well characterized. This study uses computational models of the human body and KABs to explore how KAB design may influence the impact response of the occupant's lower extremities.Methods: The analysis was conducted using a 50th percentile male occupant human body model with deployed KABs in a simplified vehicle interior. The 2 common KAB design types, bottom-deploy KAB (BKAB) and rear-deploy KAB (RKAB), were both included. A state-of-the-art airbag modeling technique, the corpuscular particle method, was adopted to represent the deployment dynamics of the unfolding airbags. Validation of the environment model was performed based on previously reported test results. The kinematic responses of the occupant lower extremities were compared under both KAB designs, 2 seating configurations (in-position and out-of-position), and 3 loading conditions (static, frontal, and oblique impacts). A linear statistical model was used to assess factor significance considering the impact responses of the occupant lower extremities.Results: The presence of a KAB had a significant influence on the lower extremity kinematics compared to no KAB (P <.05) by providing early restraint and distributing contact force on the legs during airbag deployment. For in-position occupants, the KAB generally tended to decrease tibia loadings. The RKAB led to greater lateral motion of the legs compared to the BKAB, resulting in higher lateral displacement at the knee joint and abduction angle change (51.2 ± 21.7 mm and 15° ± 6.0°) over the dynamic loading conditions. Change in the seating position led to a significant difference in occupant kinematic and kinetic parameters (P <.05). For the out-of-position (forward-seated) occupant, the earlier contact between the lower extremity and the deploying KAB resulted in 28.4° ± 5.8° greater abduction, regardless of crash scenarios. Both KAB types reduced the axial force in the femur relative to no KAB. Overall, the out-of-position occupant sustained a raised axial force and bending moment of the tibia by 0.8 ± 0.2 kN and 21.1 ± 8.7 Nm regardless of restraint use.Conclusions: The current study provided a preliminary computational examination on KAB designs based on a limited set of configurations in an idealized vehicle interior. Results suggested that the BKAB tended to provide more coverage and less leg abduction compared to the RKAB in oblique impact and/or the selected out-of-position scenario. An out-of-position occupant was associated with larger abduction and lower extremity loads over all occupant configurations. Further investigations are recommended to obtain a full understanding of the KAB performance in a more realistic vehicle environment.

Evaluation of driver lower extremity injuries in 16 oblique crashes with THOR

Injuries to the lower extremity (LE) continue to occur in frontal crashes despite increased attention on the vehicle structure and restraint design. This study focuses on thigh, leg, foot, and ankle injuries as well as occupant factors and intrusion levels. Sixteen vehicles, including three same types, with same moving deformable barriers of the same mass, velocity, and barrier face properties, and the same occupant Test Device for Human Occupant Restraint (THOR) 50th percentile adult male in the driver's seat were used to conduct oblique impact test. Data from the left (driver side) oblique crash tests conducted by National Highway Traffic Safety Administration (NHTSA) were used in this paper to analyse the detailed intrusion characteristics and the driver side THOR injuries from head to foot in these 16 tests. Different regions of the THOR dummy were analysed. Maximum values of all lower extremity injury criteria were obtained and analysed. Intrusion and lower extremity injuries correlation was found, knee airbag and lower extremity injury correlation was also analysed. The foot-well X and Y intrusions in the 16 tests rank from minimum 14 to maximum 309 mm and from −7 to 184 mm, independently. Sixty-nine per cent right knee displacement is greater than the left knee displacement. Thirty-one per cent knee displacement and 44% left upper tibia force of the 16 tests have values that exceed injury assessment reference values. Left upper tibia force was generally greater than other tibia forces. Half of the left upper tibia index (TI) and 37.5% of the right lower TI do not meet the standard value. The foot/ankle complex is generally at a higher risk than the other parts of the leg. Same vehicle reproducibility and injury were also analysed. Right knee displacement, left femur force, left upper tibia force, left upper TI, and left ankle rotation are the most critical injuries in the respective regions of the lower extremity. Intrusion may be more prominent in some frontal damage types than in others, but not the only reason for lower extremity injuries. Other factors that influence LE injuries are the position of driver foot, the geometry of the foot-well area, the direction of intrusion, the impact energy, and acceleration of the floor. Lower extremity is the most frequently injured body region with respect to more serious injuries in the analysed test data.

An Optimization Design of Knee Airbag for Driver Protection from Inter-City Coach Frontal Impact

&lt;strong&gt;In order to &lt;/strong&gt;&lt;strong&gt;reduce the injury risk of driver’s lower extremities, a driver knee airbag was de&lt;/strong&gt;&lt;strong&gt;veloped&lt;/strong&gt;&lt;strong&gt; and optimized by&lt;/strong&gt;&lt;strong&gt; using mathematical models&lt;/strong&gt;&lt;strong&gt;. The influence of eight design parameters of belt and knee airbag on the injuries of driver’s lower extremities was analyzed. The &lt;/strong&gt;&lt;strong&gt;result &lt;/strong&gt;&lt;strong&gt;shows that the key influence factors&lt;/strong&gt;&lt;strong&gt; &lt;/strong&gt;&lt;strong&gt;are&lt;/strong&gt;&lt;strong&gt; sensitive to the injuries of lower extremity&lt;/strong&gt;&lt;strong&gt;, including initiation &lt;/strong&gt;&lt;strong&gt;timing &lt;/strong&gt;&lt;strong&gt;of knee airbag,&lt;/strong&gt;&lt;strong&gt; the strap length of knee airbag and area coefficient for the exhaust openings of knee airbag&lt;/strong&gt;&lt;strong&gt;. Based on multi-objective genetic algorithms&lt;/strong&gt;&lt;strong&gt;,&lt;/strong&gt;&lt;strong&gt; an optimization of the knee airbag was conducted in terms of the three factors. After optimization, the injury risk of driver’s lower extremities is greatly reduced.&lt;/strong&gt;&lt;strong&gt;&lt;/strong&gt;

The association between knee airbag deployment and knee–thigh–hip fracture injury risk in motor vehicle collisions: A matched cohort study

IntroductionIn the U.S. alone, an estimated 30,000 knee–thigh–hip (KTH) injuries occur annually in frontal motor vehicle collisions. These fractures typically occur through occupant contact with the vehicle's knee bolster. Research has suggested that knee airbags (KABs) can mitigate the forces sustained during this contact, resulting in decreased injury risk; however, previous research has been limited by small sample sizes or by occurring in a controlled setting. The objective of the current study is to determine the effectiveness of KABs on KTH fracture risk using nationally representative, real-world data. MethodsUsing combined data from the Crash Injury Research and Engineering Network and the National Automotive Sampling Survey, a matched cohort study was conducted among front-seat occupants of vehicles involved in a frontal collision occurring from 2000 to 2009. Occupants exposed to a KAB deployment were matched to occupants with no KAB deployment based on age ±5 years, sex, seatbelt use, vehicle seating position (i.e., driver or front passenger), car vehicle body type, collision impact, and sampling weight. A Cox proportional hazards model was used to calculate risk ratios (RRs) and associated 95% confidence intervals (95% CI) to estimate the association between KAB deployment and lower extremity fracture risk. ResultsThere was no association between KAB deployment and risk of lower extremity fracture (RR 0.83, 95% CI 0.52–1.31). A notable pattern in fracture risk, though not statistically significant, was observed, with a decreased risk of hip (RR 0.72, 95% CI 0.26–1.97) and thigh fracture (RR 0.81, 95% CI 0.32–2.05), and an increased risk of tibia/fibula (RR 1.23, 95% CI 0.52–2.90) and foot fracture (RR 1.96, 95% CI 0.72–5.32). ConclusionsThe results of the current study suggest that KABs are not associated with the risk of lower extremity fractures. However, given the small sample size of the current study, it is difficult to definitively say whether the observed injury pattern is representative of the true pattern.

Larger-volume knee airbag increases occupant safety

Now that front, side, and window airbags are common, accident researchers and safety experts have turned their attention to the footwell, up to now relatively unprotected. Autoliv has developed a knee airbag that restrains the lower extremities in good time, considerably reducing the loading on the knees and pelvic region. At the same time it reduces the risk of the head making contact with the windscreen or A pillar.