Aspects regarding ocupant safety in the rear end collision.

Benea, Bogdan ; Trusca, Daniel ; Soica, Adrian 等

1. INTRODUCTION

For simulate impact between two cars has been used dedicated software PC-Crash DSD, Linz, Austria.

To determinate varying of accelerations at head and torso level in correlation with pushing vehicle speed was simulated front-rear collision between two vehicles with a speed between 15 km/h and 70 km/h.

Neck injury criteria is value what correlate moving of head relative to cervical vertebra (T1 cervical vertebra) with spinal ganglia injury.

NIC index is a good assessment criteria of whiplash injury. Calculate NIC:

NIC = 0.2 x [a.sub.rel] + [v.sup.2.sub.rel] (1)

[a.sub.rel] = [a.sup.T1.sub.x] - [a.sup.Cap.sub.x] (2)

[v.sub.rel] = [integral] [a.sub.rel] dt (3)

where:

NIC = neck injury criteria

[a.sub.rel] = relative acceleration between head and torso

[v.sub.rel] = relative speed between head and torso

[FIGURE 1 OMITTED]

Analyzing figure 2 peak value of NIC varying between 70 and 12 [m.sup.2]/[s.sup.2] for a vehicle speed between 70 and 15 km/h. Neck injury criteria is a good indicator of whiplash injury probability. A modeling software enables to investigate various parameters who influence injury of passenger form vehicle concerned in collisions.

[FIGURE 2 OMITTED]

Growing the pusher vehicle's speed or relative speed between vehicles determines a direct proportional growing of injury probabilities.

2. EXPERIMENTAL STUDY

For experimental testes it considers a rear collisions. Hypotheses for experimental testing:

A vehicle is stationary (zero speed).

The pusher vehicle speed is between 15 and 70 km/h

The driver of the stationary vehicle is a dummy.

In order to fulfill the tests, a series of equipment and devices were used, as follows:

* motor vehicle OLTCIT CLUB 12TRS;

* motor vehicle FIAT CROMA 1.9 i.e.;

* a dummy designed and constructed for this type of tests within the Laboratories of the Department of Vehicles and Engines;

* data acquisition and processing system;

* high-speed camera;

* electrical and networking equipment;

* equipment for mechanical and auto repairs;

* measuring/quoting the surface designed for experiments;

* protection and first aid equipment in case of accidents at the work place.

The vehicles were prepared for tests as follows:

* The fuel was taken out of the tank for safety reasons;

* The seatbelt system for the front left seat was carefully checked;

* During the tests, the 5th wheel was mounted to determine the traveling speed;

* The Data logger OMEGA SHOCK101 and the DSD Pocket DAQ device were mounted according to the axes of the general octagonal reference system chosen

It was made two tests:

* Test 1

--Dummy wears seatbelt

--Headrest in lower position

--V = 19.44 km/h

* Test 2

--Dummy wears seatbelt

--No headrest

--V = 14.77 km/h

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

During test, the torso's acceleration respects the car's acceleration with a 30 ms delay. The delay appears through seat's amortization. The delay between maximum acceleration of head and torso is 60 ms.

Both seat's amortization and wrong usage of headrest heighten injury possibility with 22% of whiplash injury.

During impact, after accelerations transmission between cars and seat, the acceleration is gradualy assumed by the thorax, and through the kinematic chain to head. Peak maximum head acceleration is achieved when the movement towards chest seat is maximum.

Body movement of occupant of the chair continues to return to its original position, with a maximum displacement of the head-direction on--x and -z direction.

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

Occupant head motion continues with changing direction of travel and chin bringing into contact with the chest.

Opposed extension mechanism, flex can produce most common injuries of the spine. During application, the neck muscles transmit task, making the distribution of force to the other structures of the neck. Thus, the request from the head causes a redistribution of the burden of the neck, which may reduce potential injury to the neck.

Shearing forces of neck flexion are important before the chin hits the chest.

When the chin encounters the breast occurs a redistribution of tasks. Chin-chest contact makes an interior force to develop muscle size for the same post when bending. In addition, the force has a component that is parallel to the shearing force developed by the neck and that emphasized the head deceleration.

Incorrect positioning of the headrest or the lack of this element of passive safety, even at a low speed of the car produces an emphasized displacement of the head relative to torso that means an increased likelihood of neck injury.

3. CONCLUSIONS

Using virtual simulation programs is a necessary tool in analysis and reconstruction of road accidents. The comparison between data obtained from simulation and experimental study have shown a coincidence between the time producing characteristic moments such as the emergence maximum acceleration head and thorax.

In addition, size variation is oscillating in the experiment; this is due to greater elasticity of the seat and the vehicle structure.

Results were similar to the maximum amount of NIC criterion: 17 [m.sup.2]/[s.sup.2], compared to 18 [m.sup.2]/[s.sup.2].

Transmission of acceleration between vehicle and occupant is made across kinematic chain-vehicle head-torso, producing a relative movement between head and torso, which occurs over a joint liaison between the two components of the kinematic chain, the likelihood of whiplash injury increased from 85 % An incorrect adjustment or missing of safety devices can lead to worse consequences of road events, even if impact speeds are relatively low.

The absorption system of seat must take into account by moving attenuation in kick moving by implementing an absorption system of post impact forces apportioned between body and seat.

4. REFERENCES

Datentechik, S (2008). PC-CRASH A Simulation Program for Vehicle Accidents, Technical and Operating Manual, Version 8.2--November 2008, Linz, Austria

Gaiginschi, R. & Filip, I. (2002). Technical Expertise of Road Accidents, Technical Publishing, Bucharest, 2002

Soica A.; Lache S. (2007). Theoretical and Experimental Approaches to Motor Vehicle--Pedestrian Collision, 3rd WSEAS '07, Tenerife, Canary Islands, Spain, December 14-16, ISSN 1790-2769, pp 264-270

Soica, A.; Motoc Luca, D.; Lache, S. & Tarulescu, S. (2008). Aspects Concerning of the Vehicle-Pedestrian Impact at Low Velocities, Daaam International Scientific Book 2008, pp 797-810

Trusca D.D., (2008). Research on Improving Passive Safety Car in Rear End Collision--PhD thesis

Volker E., Sferco R., Fay P.--A Detailed Analysis of the Characteristics of European Rear Impacts. Ford Motor Company, Germany and UK Paper Number 05-0385