Influence of seat characteristics on occupant motion in low-speed rear impacts

doi:10.1016/S0001-4575(99)00082-2

Accident Analysis & Prevention

Volume 32, Issue 2, March 2000, Pages 243-250

https://doi.org/10.1016/S0001-4575(99)00082-2 Get rights and content

Abstract

To analyze the effect of the seat characteristics on dummy motions and human volunteer motions, sled tests simulating low-speed rear impacts were conducted with some seats which had different characteristics. Volunteer’s cervical vertebral motions were photographed with an X-ray cineradiographic system at a speed of 90 frames/s as well as the visible motions of dummy’s and volunteer’s were recorded. Although the tests were conducted under limited conditions, the results indicated the relationship between the occupant’s visible motions, which are assumed to be closely related to the whiplash injury mechanism, and seat characteristics. It should be noted that the volunteer sled tests were discussed and approved by the Tsukuba University Ethics Committee and the volunteer submitted his informed consent in writing in line with the Helsinki Declaration.

Introduction

The numbers of people killed and injured in traffic accidents in Japan in 1996 are broken down into percentages in Fig. 1 according to the direction of impact (Japan Traffic Safety Association, 1997). These data indicate the characteristics of vehicle occupant fatalities and injuries in traffic accidents in Japan. The largest number of fatalities occurred in frontal impacts, followed by side impacts, with very few fatalities occurring in rear impacts. In contrast, the largest number of injuries occurred in rear impacts, which accounted for nearly one-half of the total. This tendency was completely different from the results seen for fatalities. An investigation of the nature of the injuries suffered in rear impacts revealed that approximately 90% were neck injuries, which accounted for approximately 44% of all injuries (Fig. 2). It will be noted that these same tendencies were also observed in 1997 traffic injury data (Fig. 3).

According to a report based on traffic accident data compiled in Germany, over 90% of such neck injuries in rear impacts occur at ΔV (change of velocity of struck car) ≤25 km/h (Eichberger et al., 1996). This indicates that neck injuries are a characteristic of low-speed rear impacts.

Whiplash neck injuries that occur in low-speed rear impacts are thought to be related to automotive seat characteristics (Olsson et al., 1990, Ono et al., 1993, Song et al., 1996). For this reason, it is very important to know how seat characteristics affect occupant motions in low-speed rear impacts. Since vehicle occupants are mainly restrained by the seatback and the head restraint in low-speed rear impacts, the position of the head restraint and the stiffness distribution of the seatback are selected as parameters expressing seat characteristics in this research.

Section snippets

Injury mechanism

It has generally been accepted that hyperextension of the neck is the cause of whiplash, and research has been conducted to examine the tolerance of humans to hyperextension of the neck (Mertz et al., 1971). The results of recent studies have shown, however, that factors other than hyperextension also deserve attention (Matsushita et al., 1994). It has been reported that whiplash can occur even in situations that do not lead to hyperextension (Svensson et al., 1993, Bostrom et al., 1996, Ono et

Materials

Table 1 gives the specifications of the six seats used in the sled tests.

Seat A was a standard seat. Standard seat means a front seat designed for a small passenger car.

Seat B was created by adding a mechanical linkage system to seat A. As illustrated in Fig. 5, the linkage system used the occupant’s inertial force at the time of impact to move the head restraint forward and upward. In other words, the head restraint of seat B was ordinarily in the same position as that of the other seats, and

Test method

Using the sled test setup shown schematically in Fig. 8, sled impact tests were conducted that simulated low-speed rear impacts. These tests were conducted under conditions equivalent to the change of velocity ΔV=25 km/h, because it has been reported that over 90% of all neck injuries in rear impacts occur at the change of velocity ΔV≤25 km/h (Eichberger et al., 1996). Specifically, the sled impact velocity was V₀=20 km/h and the post-impact reaction velocity was approximately 5 km/h.

The impact

Test method

Using the sled test setup shown schematically in Fig. 12, tests that simulated low-speed rear impacts were conducted with a volunteer. To ensure the safety of the volunteer, the sled impact velocity was set at V₀=8 km/h based on previous test data (Ono et al., 1997). Measurements were made of the volunteer resultant acceleration and visible motions captured by a high-speed video camera about all seats. About seats A and B, cervical vertebral motions were also recorded by X-ray cineradiography

Conclusions

This study examined the visible motions of a vehicle occupant thought to be closely related to the mechanism of whiplash. The influences of seat parameters on dummy responses in low-speed rear impacts were analyzed with respect to these visible motions. An analysis was also made of data recorded in sled impact tests conducted with a human volunteer. The results made clear the following points under the limited test conditions used in this study.

(1) The position of the head restraint influenced

Acknowledgements

The authors would like to thank Institute for Traffic Accident Research and Data Analysis (ITARDA) for letting us use the traffic accident data.

References (12)

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Eichberger, A., Geigl, B.C., Moser, A., Fachbach, B., Steffan, H., 1996. Comparison of Different Car Seats Regarding...
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Matsushita, T., Sato. T.B., Hirabayashi, K. 1994. X-Ray Study of the Human Neck Motion Due to Head Inertia Loading, SAE...
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