Head dynamics during emergency braking events

SAE International journal of transportation safety, 2022

Whiplash injuries resulting from vehicle collisions are still a significant socioeconomic issue across the world. Years of research has resulted in the development of injury criteria, restraint systems and a deeper understanding of the injury mechanism. However, some grey areas remain and, in the context of the increasing automation of vehicles, one can wonder how the injury mechanisms may change due to changes in collision forces or directions. This paper presents an experiment with ten volunteers subjected to two braking modes, including automated braking preceded by an alarm warning or robot human braking, in three different initial head positions: forward facing, lateral rotation and flexion rotation. The volunteers were equipped with inertial measurement units to record their head and neck dynamics. Results show that the initial position of volunteers implies differences in the volunteer head dynamics. Also, the auditory alarm emitted prior to the emergency braking may have helped the volunteers to mitigate the mechanical stimulus and most likely the injury risk.

Traffic Injury Prevention, 2018

Objective: A test track study was conducted to quantify patterns of adult front seat passenger head motion during abrupt vehicle maneuvers. Method: Eighty-seven men and women with a wide range of body sizes and ages participated in data collection on a closed test track in a passenger sedan under manual control by a test driver. Because a primary goal of the study was to gather "unaware" data, the participants were instructed that the study was concerned with vehicle dynamics and they were required to read from a questionnaire taped to the top of their thighs as the drive began. The first event was a hard brake (approximately 1 g) to a stop from 35 mph (56 kph). Within the space of approximately 5 min the participants also experienced an aggressive lane change, a sharp right turn with simultaneous hard braking, and a second hard braking event. A Microsoft Kinect v2 sensor was positioned to view the area around the front passenger seat. Head location was tracked using the Kinect data with a novel methodology that fit 3D head scan data to the depth data acquired in the vehicle. Result: The mean (standard deviation) forward excursion of the estimated head center of gravity (CG) location in the first braking event was 135 (62) mm. The forward head CG excursion in the second braking event of 115 (51) mm was significantly less than that in the first, but the difference was small relative to the within-condition variance. Head excursion on the second braking trial was less than that on the first trial for 69% of participants. The mean maximum inboard head excursion in lane-change maneuvers was 118 (40) mm. Forward head excursions in braking were significantly smaller for older passengers and those with higher body mass index, but the combined factors accounted for less than 25% of the variance. Inboard head excursion in the lanechange event was significantly related to stature, but only about 7% of variance was related to body size. Head excursions for men and women did not differ significantly after accounting for body size. Discussion: This is the first quantitative occupant dynamics study to use a large, diverse sample of passengers, enabling the exploration of the effects of covariates such as age and body size. Conclusions: The data demonstrate that a relatively large range of head positions can be expected to result from abrupt vehicle maneuvers. The data do not support simple scaling of excursions based on body size.

Driving Simulation Conference & Exhibition, 2019

This paper presents a pilot study which aims at comparing the results of dynamic ranges of motion made in real conditions versus virtual conditions. Whiplash remains a big socioeconomic issue and the need to implement virtual reality to better understand the head stabilization strategies is here spelled out. To do so, we proposed two experiments in which subjects are seated on the front passenger seat and are subject to a given deceleration. The vehicle accelerates to a given speed, maintain its speed for a short time then proceed to the braking event which is either a custom one or the natively equipped emergency automated braking system. Range of motion and acceleration of the head are recorded. The final goal of the study is to replicate the experiment on a hexapod driving simulator. We expect the results of this replication to legitimate the comparison between results from real tests and results obtained using driving simulators. Doing such tests should reduce their human and technical costs and give a better knowledge of the participant cognition by the perfect control of the visual environment.

Driving Simulation Conference, 2019

This paper presents a pilot study which aims at comparing the results of dynamic ranges of motion made in real conditions versus virtual conditions. Whiplash remains a big socioeconomic issue and the need to implement virtual reality to better understand the head stabilization strategies is here spelled out. To do so, we proposed two experiments in which subjects are seated on the front passenger seat and are subject to a given deceleration. The vehicle accelerates to a given speed, maintain its speed for a short time then proceed to the braking event which is either a custom one or the natively equipped emergency automated braking system. Range of motion and acceleration of the head are recorded. The final goal of the study is to replicate the experiment on a hexapod driving simulator. We expect the results of this replication to legitimate the comparison between results from real tests and results obtained using driving simulators. Doing such tests should reduce their human and technical costs and give a better knowledge of the participant cognition by the perfect control of the visual environment.

Annals of Biomedical Engineering

Occupants exposed to low or moderate crash events can already suffer from whiplash-associated disorders leading to severe and long-lasting symptoms. However, the underlying injury mechanisms and the role of muscle activity are not fully clear. Potential increases in injury risk of non-nominal postures, i.e., rotated head, cannot be evaluated in detail due to the lack of experimental data. Examining changes in neck muscle activity to hold and stabilize the head in a rotated position during pre-crash scenarios might provide a deeper understanding of muscle reflex contributions and injury mechanisms. In this study, the influence of two different head postures (nominal vs. rotation of the head by about 63 ± 9° to the right) on neck muscle activity and head kinematics was investigated in simulated braking experiments inside a driving simulator. The braking scenario was implemented by visualization of the virtual scene using head-mounted displays and a combined translational-rotational pl...

2018

Up to 80% of crashes are preceded by pre-crash maneuvers such as emergency braking. Precrash maneuvers, which may avoid or mitigate crashes, also may influence passenger kinematics and lead to less optimal positioning if a subsequent crash occurs. Previous research has documented driver kinematics during automatic braking. Yet, passenger response to automated emergency braking is less understood. This is also relevant for those in the rear seat who may not anticipate the braking event. Thus, we compared rear passenger kinematics for pediatric and adult human volunteers in driver-applied manual emergency braking (MEB) and automated emergency braking (AEB) via closed track testing. 18 participants (5 adults (age 22.0 ±1.9 years), 7 teens (age 14.9 ±1.2 years), 6 children (age 10.8 ±1.6 years)) were seated in the rear right passenger seat of a modern 4-door sedan. Steady-state head and sternum displacement and peak rate of change of displacement were compared across maneuvers. As a met...

Biofidelic human body models (HBMs) with active muscles are valuable tools for assessing the safety potential of systems that are active immediately before and during a crash. For validation, experimental data including muscle activity are required. This paper provides a data set for front seat passengers in autonomous braking events comprising 20 volunteers (11 male and 9 female) in a passenger car. Volunteers were subjected to two different autonomous braking test cases of 1.1 g, wearing a standard belt and a reversible pre-tensioned belt activated 200 ms before deceleration onset. The following data were collected: muscle activity with electromyography, kinematics with video tracking, footwell force, belt force and belt payout. Head and T1 displacements were shorter with a pre-tensioned belt while head rotation was similar for both test cases. Kinematics did not display any significant gender differences. Average muscle activity with a pretensioned belt increased rapidly before onset of deceleration for females, but not for males. Muscle activity, predominantly in the cervical and lumbar extensors, increased soon after vehicle deceleration onset for all volunteers wearing the standard belt. All muscles were significantly more active during braking than normal driving. Data are presented in corridors for use when validating active HBMs.

Traffic Injury Prevention, 2019

Objective: Emergency braking can potentially generate precrash occupant motion that may influence the effectiveness of restraints in the subsequent crash, particularly for rear-seated occupants who may be less aware of the impending crash. With the advent of automated emergency braking (AEB), the mechanism by which braking is achieved is changing, potentially altering precrash occupant motion. Further, due to anatomical and biomechanical differences across ages, kinematic differences between AEB and manual emergency braking (MEB) may vary between child and adult occupants. Therefore, the objective of this study was to quantify differences in rear-seated adult and pediatric kinematics and muscle activity during AEB and MEB scenarios. Methods: Vehicle maneuvers were performed in a recent model year sedan traveling at 50 km/h. MEB (acceleration 1 g) was achieved by the driver pressing the brake pedal with maximum effort. AEB (acceleration 0.8 g) was triggered by the vehicle system. Inertial and Global Positioning System data were collected. Seventeen male participants aged 10-33 were restrained in the rear right passenger seat and experienced each maneuver twice. The subjects' kinematics were recorded with an 8-camera 3D motion capture system. Electromyography (EMG) recorded muscle activity. Head and trunk displacements, raw and normalized by seated height, and peak head and trunk velocity were compared across age and between maneuvers. Mean EMG was calculated to interpret kinematic findings. Results: Head and trunk displacement and peak velocity were greater in MEB than in AEB in both raw and normalized data (P .01). No effect of age was observed (P .21). Peak head and trunk velocities were greater in repetition 1 than in repetition 2 (P .006) in MEB but not in AEB. Sternocleidomastoid (SCM) mean EMG was greater in MEB compared to AEB, and muscle activity increased in repetition 2 in MEB. Conclusions: Across all ages, head and trunk excursions were greater in MEB than AEB, despite increased muscle activity in MEB. This observation may suggest an ineffective attempt to brace the head or a startle reflex. The increased excursion in MEB compared to AEB may be attributed to differences in the acceleration pulses between the 2 scenarios. These results suggest that AEB systems can use specific deceleration profiles that have potential to reduce occupant motion across diverse age groups compared to sudden maximum emergency braking applied manually.

2015

The motivation of this project was to develop a three level neutral point clamped (NPC) traction inverter for a permanent magnet synchronous machine drive. The three-level inverter helps to reduce the total inverter losses at higher switching frequencies, compared to a two-level inverter for electric vehicle applications. The three-level inverter has also more power switches compared to the two-level inverter. This helps to reduce the voltage stress across the switches and the machine winding. In addition, it also allows an increase in the DC-link voltage, which in turn helps to reduce the DC-link current, phase conductor size and the associated losses. Moreover, at higher DC-bus voltages the power switches will have lower thermal stress when compared to the 2-level. However, the NPC inverter topologies have an inherent problem of DC-link voltage balancing. In the initial part of this thesis, a novel space vector based DC-link voltage balancing strategy is proposed. This strategy ca...

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