Interpretation ID: nht72-4.25

DATE: 09/18/72

FROM: AUTHOR UNAVAILABLE; Richard B. Dyson; NHTSA

TO: British Standards Institution

TITLE: FMVSS INTERPRETATION

TEXT: This is in further reply to your letter of July 26, 1972, concerning the seat belt retractor test protector test procedures of section S5.2(k) of Motor Vehicle Safety Standard No. 209.

In our initial reply of August 21, we stated that the belt was to be retracted completely during the cycling, even though some vehicle installations might prevent complete retraction. After further examining the consequences of this position, we have concluded that it is in error.

The intent of the cycling sequence is to reflect the normal use of the belt over time. If the belt is designed to be installed in a vehicle in such a manner that during normal cycling a part of the webbing cannot be wound onto the retractor, a compliance test should employ the same restrictions of movement. We therefore conclude that you are correct in considering a belt to be fully retracted for purposes of Standard No. 209 when it is retracted as fully as the geometry of its installation permits.

Sincerely,

L R Schneider -- Chief Counsel, US Department of Transportation, 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, RAC DANDY --Senior Engineer Head of Mechanical Section