Interpretation ID: nht72-4.27

DATE: 01/01/72 EST.

FROM: AUTHOR UNAVAILABLE; Richard B. Dyson; NHTSA

TO: British Standards Institution

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your letter of July 26, 1972, on the subject of seat belt retractor testing under S5.2(k) of Motor Vehicle Safety Standard No. 209.

Your outline of the emergency locking retractor test procedure is essentially correct. During the initial 5,000 cycles, however, the belt is to be retracted completely, even though some vehicle installations may prevent complete retraction. The assumption in (3)(ii) of your letter is therefore incorrect.

The remaining points in your interpretation are correct.

Sincerely,

ATTACH.

British Standards Institution

L R Schneider -- Chief Counsel, U S Department of Transporatation, National Highway Traffic Safety Administration

JULY 26, 1972

Dear Sir

F M V S S 209

We are writing as a National Test Laboratory concerned with automotive safety testing and, in particular, seat belt assemblies to your specifications. Some parts of the specification are open to interpretation and we are, of course, concerned that we should operate our test procedure in the accepted manner.

In particular, we would request that you confirm our test methods in connection with Clause S5.2(k) "Performance of retractor". In the case of emergency locking retractors, we proceed as follows:-

1) Corrosion test.

2) Manual withdrawal retraction for 25 cycles.

3) 2500 cycles from full extension to full retraction with an application of 20 lbs force at full extension.

Note (i) As this force is dynamically applied, the mass concerned is less than 20 lbs.

(ii) Full retraction is assumed to mean the full possible retraction of the assembly when installed in a motor vehicle. This will be less than the capability of the retractor, but reflects the practical conditions providing the installation data is obtained from the belt submittor.

4) Temperature resistance test.

5) 2500 additional cycles as (3).

6) Dust test.

7) Manual withdrawal and retraction for 25 cycles.

8) For emergency locking retractors, 45000 cycles operated between the limits of 50% extraction and 100% extraction.

Note (i) The stroke will therefore be half of that applied for the initial 5000 operations and will fully extract the webbing on each occasion.

(ii) Because full extraction occurs, the 20 lbs force will be applied during the 45000 operations as well as the previous 5000 operations.

9) During the initial 5000 operations, 1000 locking operations occur and during the final 45000 operations, 9000 locking operations occur. The locking operations are applied at any point between 50% extraction and 100% extraction.

10) The 20 lbs force is applied on every cycle including the locking cycles.

We should be grateful for your assistance in this matter as a considerable quantity of test work is awaiting clarification of this particular test procedure.

Yours faithfully for Director

R A C DANDY -- Senior Engineering; Head of Mechanical Section