Pre impact Influence on the Standard Seat belted and Motorized Seat belted Occupants in Frontal Collisions based on Anthropometric Test Dummy Susumu Ejima 1, Daisuke Ito 1, Jacobo Antona 1, Yoshihiro Sukegawa 1, Hisao Ito 1 Abstract The posture of a driver is varied according to age, gender and physique. In addition, this posture further changes just before the collision, due to a driver s evasive maneuvers. In reality, it is difficult for drivers to maintain the standard posture of the Anthropomorphic Test Dummy (ATD). Therefore, it is predicted that these behavioral differences before frontal collisions affect the gravity of injuries suffered by the occupant. The objective of this study is to investigate the influence of braking just before the collision in the frontal impact test with a dummy while considering the effect of the belt restraint system. Keywords Pre crash, Sled, Occupants, Restraint Systems, Anthropometric Test Dummy I. INTRODUCTION In this research, the effect of occupant protection systems is evaluated by tests with an ATD applying the pre crash conditions. So far, such evaluation was usually done by computer models [1] because it was difficult to reconstruct the circumstances of the pre crash phase in the laboratory. However, it is now possible to evaluate the effects of leading edge safety devices such as the smart restraint system and the adaptive restraint system by way of laboratory experiment. Therefore, the authors propose the experimental effect evaluation method with the test sled that can incorporate the influence of braking in the pre crash phase. In this experimental system, the barrier test which was employed in the traditional frontal impact tests was improved so that a crash stop could be given just before the collision against the barrier. The ATD for the effect evaluation of occupant protection devices was also improved so that it could replicate the driver s behavior at the time of a low impact collision. In the experiment in which the mass produced three point seat belt (SB) was fitted to the improved ATD, it was confirmed that braking in the pre crash phase enhances the impact forces on the chest and pelvis. In addition, for the effect evaluation of the occupant protection devices, a motorized seat belt (MSB) which was equipped with a motor in the retractor was employed as a device to retract the webbing for restraining the posture at the time of braking. II. METHODS Development of Pre Crash Sled System The objective of the development of the pre crash sled is to assess the pre crash behavior of the driver and the influence on the driver after the collision either when the occupant protection device such as the MSB coupled with pre crash brake is activated or when the driver steps on the brake pedal. Figure 1 shows the Impact absorber Rigid Barrier Pre-crash sled Running Cutting off from the pulling unit (Pulling by the wire) Velocity Crash Fixed barrier time ECE corridor Cylinder Pipe (Aluminum) Up to 1G Deceleration Fig. 1. Concept of crash experiment with pre impact braking Fig. 2. Pre impact braking sled apparatus - 31 -
concept of the crash experiment with the pre crash sled system. This pre crash sled (Figure 2) is a decelerating sled with a braking system, and the experiment is done on the rail for a frontal collision. In this experiment, the pre crash sled is tugged by the pulling unit of the collision test facility until it reaches the prescribed running speed. Then the sled is released at the setup point from the pulling unit. Finally the sled is impacted with braking deceleration against the shock absorber in front of the fixed barrier. In this test, the pre crash sled was running at the speed of 67 km/h, braking started with.8 G, and after around.873 seconds, the sled collided at the speed of 48 km/h. It is necessary to reconstruct the driver s posture change caused by pre crash braking by means of a dummy. In this experiment, Hybrid 3 is employed as the dummy for the impact test. Before the experiment, an impact simulating the harsh braking was given to the dummy, and the forward bending behavior of the dummy was compared with the data from the volunteer tests. As a result, the forward bending characteristics of the dummy were improved by changing the mechanical property of the lumber rubber tube. Because muscle reaction is not considered in the dummy, the results of the lower impact frontal collision volunteer test in a relaxed state were employed [2]. In this test, a constant acceleration 8.m/s 2 (duration ms) was given to the 4 male volunteers using the horizontal sled. In order to compare the forward bending behavior with that of the driver, a lower impact test was implemented with the dummy under the same conditions as the volunteer test. Figure 3 shows the experiment apparatus. The biofidelity evaluation of the flexion features of the dummy was done by the comparison between the volunteers and the dummy by using the flexion angle history of the upper torso against the thighs in Figure 3. Figure 4 shows the comparison of the time history of the flexion angles between the dummy and the volunteers. The flexion features of the 4 volunteers are indicated by their corridors (dotted gray line: ±1SD) and the flexion feature of the improved dummy with the thick black line, while the normal features of the dummy are indicated by the thin gray line. Compared with the dummy with the original lumbar feature, the dummy with the improved lumbar feature indicates better flexion angle, and the maximum flexion angle and the angle history are close to those of the volunteers. As a result of this improvement of the lumbar feature of the dummy, it became possible to reconstruct the forward bending behavior of the human torso at the time of braking. T1 Hip T1 Hip Fig. 3. Pre impact simulation sled illustrating the flexion angle Angle[deg] 5 45 35 3 25 15 1 5 HY-3 HY-3 (Modified Lumber) Volunteer Corridor +SD Volunteer Corridor -SD 1 3 5 Time[ms] Fig. 4. Time history of the flexion angle of the upper body with respect to the femoral region Japan Automobile Research Institute, 253 Karima, Tsukuba, Ibaraki Japan, 35 822 Tel:+81 29 856 883, Fax: +81 29 856 1135 e mail: sejima@jari.or.jp - 32 -
Test Scenario In order to examine the influence of the braking in the pre crash phase, three tests are implemented employing mass produced seat belts. In this Scenario 1 Speed: 67 km/h research, three scenarios shown in Figure 5 were.8 G established focusing on the influence of braking Scenario 2 and the effect of the motorized seat belt. The Speed: 67 km/h details of the scenarios are as follows: a) Scenario 1 (With braking (SB)): The running.8 G speed of the sled is decelerated from 67 km/h to 48 km/h by braking, and then the sled collides against the barrier with the SB. b) Scenario 2 (With braking (MSB)): The running speed of the sled is decelerated from 67 km/h to 48 km/h by braking, and then the sled collides against the barrier with the MSB. Scenario 3 Speed: 48 km/h Fig. 5. Test Scenarios c) Scenario 3 (Without braking (SB)): The sled collides against the barrier at the speed of 48 km/h with SB. III. RESULTS Restraint System Mass-produced Motorized Mass-produced Figure 6 shows the comparison of the dummy s posture change in Scenarios 1 and 2. The posture control effect of the MSB is shown by comparing the seating postures, which were measured by the high speed camera. Figure 6(a) indicates the dummy s seating posture with the representative points of each part of the body. In addition, the stick figures indicate the amount of the movement at every ms from the time of braking in Figure 6(b) and (c). The " Start" ( 873ms) indicates the posture at the starting time of braking while the "Target Marker Posture" indicates the posture at the time of collision (ms). In Figure 6(b), the dummy s torso at the time of collision is bending due to the inertial force, which is different from its posture at the time of Start. On the other hand, it can be confirmed that because the MSB s activation is synchronized with the starting time of braking, the dummy s posture is similar to its initial seating posture at the time of collision against the barrier (Figure 6(c): ms). In addition, the MSB worked effectively on the dummy s posture change because the amount of posture change of the dummy with the MSB at around 6ms is smaller than that of the dummy with the SB. This figure also indicates the difference of the dummy s behavior on the head CG and the chest, which shows rather big motions in a frontal collision. By activating the MSB at the time of ms, head CG and chest are located on the right side compared with the SB. Since the amount of forward movement (X direction) is also restrained by the MSB, it can be expected that the driver can maintain the distance between his/her head and the steering wheel until the time of the collision and thereby occupant protection devices such as the airbag can work effectively. Head Top Head COG Malleolus Thigh Arm Abdomen Hip (Upper Hip (Lower) Y Coordinate [mm] 1 - ms Start Head_Top - ms ms Head_COG ms 6 ms 8 ms 1 ms Malleolus X Coordinate [mm] - Arm - Abdomen Hip(Upper) Hip(Lower) Thigh Y Coordinate [mm] 1 - ms ms X Coordinate [mm] (a) Location of target marker (b) Scenario 1 (With braking (SB)) (c) Scenario 2 (With braking (MSB)) Fig. 6. Trajectories Stick figure indicates the positions of each photo target 8 ms 1 ms 6 ms ms - ms Start - - The head and the chest are the focus of the examination of a frontal collision. Figure 7 and Figure 8 indicates the - 33 -
influence of the deceleration by braking and the effect of the MSB respectively on the amount of impact (head acceleration, chest deformation, chest and pelvis acceleration) and on the load of the shoulder belt. For the purpose of reference, the component of chest acceleration (local X and Z component) is shown in these figures. In Figure 7, the dotted line indicates the without braking case (Scenario 3), and black bar shows the relative comparison of the maximum values of the with braking case (Scenario 1). The head acceleration in the with braking case is smaller than in the without braking case. Next, the chest deformation shows no influence of the braking relative to the maximum displacement. However, since the maximum chest and pelvis acceleration and shoulder belt load in the with braking case is higher by around % than that in the without braking case, the braking in the pre crash phase exerts influence on the chest and pelvis acceleration and shoulder belt load. In Figure 8, the dotted line indicates the results with the SB (Scenario 1), while the black bar indicates the results with the MSB (Scenario 2). There is virtually no remarkable difference in head acceleration between using the MSB and the SB. However, due to the activation of the MSB at the same time of braking, chest deformation increases by up to 1% compared with the use of the SB. By the pulling force of the MSB which is forcibly pulled by the motor, the dummy chest is deformed during the pre braking. In the case of the dummy with the MSB, initial deformation is detected on the chest. On the other hand, due to the activation of the MSB, the maximum chest acceleration is decreased by around % compared with the dummy with the SB. Therefore, it appears that the restraining effect on the posture change in the pre crash phase by the MSB is reflected in chest acceleration. Finally, with regard to the occupant restraining devices, because of the lack of slack of the shoulder belt by activating the MSB, the belt load decreases. 16 1 1 With braking (SB) Without braking (=1%) 16 1 1 With braking(msb) With braking (SB) (=1%) 1 1 8 8 6 6 Head G disp G (3ms) Acc_X Acc_Z Pelvis G Belt load Head G disp G (3ms) Acc_X Acc_Z Pelvis G Belt load Fig. 7. Relative comparison of the maximum values of with braking with respect to without braking Fig. 8. Relative comparison of the maximum values of with braking (MSB) with respect to with braking (SB) IV. DISCUSSION In the case of the SB (Scenario 1) due to the inertial force, the dummy s seating posture at the time of collision (ms) is bending forwards (head CG X displacement is mm and chest X displacement is 6mm) relative to its initial posture. From this phenomenon, it can be considered that the dummy employed in this experiment reproduces the occupant s forward bending behavior in the braking phase when it is restrained by the SB. Since the dummy bends forward and the belt load is imposed on its shoulder [3], the maximum value of chest deformation is not enhanced but the chest acceleration is increased especially in the Z component (vertical). On the other hand, from the results of the pre crash experiments employing the SB and the MSB respectively under the condition of with braking, it was confirmed that the MSB has the effect not only to restrain the posture change at the time of collision but also to reduce chest and pelvis acceleration. When the pre crash sled begins to brake, the MSB simultaneously rolls up its belt by the motor and thereby restrains the upper torso of the dummy. This mechanism makes it possible for the shoulder belt to be on the appropriate position and for the dummy s chest to bend. As a result, it appears that chest resultant acceleration is decreased. V. CONCLUSIONS In this research, as one of the evaluation methods of pre crash safety technology, the pre crash sled that can reproduce the impact deceleration with braking was developed, and its features and ability were examined. In addition, the pre crash experiment with the ATD was implemented in order to examine both the influence of braking and the effectiveness of the MSB. From the results of this experiment, the differences in the pre impact braking condition governed the posture of the dummy. Due to the forward bending seating posture, the - 34 -
shoulder belt presses the dummy s shoulder part with initial tensile force. This increases the shoulder belt load, and thereby the resultant chest acceleration increases. Finally, it was also detected that the chest acceleration measured in the experiment shows the difference between the SB and the MSB with regard to the relationship between chest deformation and posture change, since the direction of the tensile force of the belt is an important factor. VI. REFERENCES [1] Iwamoto M., Nakahira Y., Kimpara H. and Sugiyama T. (9) Development of a Human FE Model with 3 D Geometry of Muscles and Lateral Impact Analysis for the Arm with Muscle Activity. SAE paper No 9 1 2266 [2] Ejima S., Zama Y., Satou F., Ono K., Kaneoka K., and Shiina I. (8) Predication of the Physical Motion of the Human Body based on Muscle Activity during Pre Impact, International Research Council on Biomechanics of Impact (IRCOBI) Conference, pp163 177 [3] Nahum A., and Melvin J. (2) Accident Injury Biomechanics and Prevention. Second edition Springer. - 35 -