The effects of pyrotechnical seat belt pretentioners on child restraints

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VTInotat

No': TF 56-02 Date: 1987-04-06

Title: The effects of pyrotechnicai seat belt pretensioners on child restraints

Author: Thomas Turbeii

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Division: Road User and Vehicie \

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Project no: 563 63-5

Sponsor: Swedish Road Safety Office (TSV)

Distribution: free I Määttä! /

Swedish Road and Traffic Research Institute

Statens väg- och trafikinstitut

' _{Pa: 58707 Linköping. Tel. 073-7752 00. Te/ex 50125 V778GI .S} Inuit Besök: Olaus Magnus väg 37, Linköping

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l INTRODUCTION

Inorder to take away the slack that reduces the protection effect of

inertia reel seatbelts, pretensioner devices have been developed. These devices are activated by animpact and will reduce the amount of slack in

the system by tensioning the belt. The most common systems today uses

pyrotechnics to roll up the slack on the retractor.

It has been questioned if these devices can be hazardous when used in

combination with child restraint systems. Due to the low mass of children

and their restraint systems it has been proposed that the forces generated

by the system might throw the child and its restraint system out of

position in a dangerous way.

2 TESTS

2.1 Dynamic tests

In order to simulate the worst case that could be expected the following configuration was used.

- The 9 kg TNO-dummy according to ECE Regulation 44. There are of course smaller children than 9 kg travelling in cars, but this dummy is

the smallest one available in which measurements can be made.

- The AKTA Loveseat rearward facing infant carrier (ECE Reg. 44

approval No. E5 02006) which has a mass of 3 kg. This device uses the

diagonal belt around the back of the seat and ought to be sensitive to

loads imposed by a pretensioner in the retractor. (See cover

illustra-tion.)

The test seat and belt geometry simulated an installation in a Volvo 700-series front passenger seat. The same type of pretensioners as used in the Volvo 780 were installed. These are pyrotechnical retractors made by

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TRW Repa in the Federal Republic of Germany. These retractors are normally triggered by a sensor with a delay of 10-15 ms after the first contact of the vehicle with an obstacle. In this case it was regarded as the worst case to trigger the device immediately at impact in order to get the infant carrier out of position and introduce a slack before the main part

of the deceleration started.

The main results from two tests made according to the tests procedures to Reg. 44 are presented below.

pretensioner pretensioner activated not activated

Test No. 536 537 Max resultant head acceleration 41 g 46 g Figure 1 Max resultant Chest acceleration 43 g 44 g Figure 2 Max force on diagonal. 2.4 kN 2.1 kb] belt Figure 3

The results show a slightly better performance when the pretensioner is in

use. The. high-speed films show no significant differences other than a few

centimetres smaller head excursion when the pretensioner is in use.

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2.2 Static test

The same test setup as before was used in a static test in order to

simu-late what might happen in the case of an inadvertant firing of the preten-sioner without a collision taking place. The results from this test were the following: pretensioner activated Test No. 540 Max resultant head acceleration 32 g Figure l ' Max resultant chest acceleration 8 g Figure 2 Max force on diagonal belt 1.4 kN Figure 3

Compared to the loads on the dummy in the dynamic test the head

acce-leration is 25% lower and the chest acceacce-leration 80% lower. The 32 g of head acceleration might seem to be high, but considering that it is a peak of short duration and that the tolerance limits used in regulations are in the 50-80 g range this head acceleration is regarded as acceptable.

Visual observations during this test showed only a slight movement of the

restraint system.

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3 CONCLUSION

Based On the tests described above the following conclusion can be made: The use of the present type of pyrotechnical pretensioners on seat belts

has no adverse effects on child restraint systems neither in a crash nor in

the case of an inadvertent firing of the system.

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