Interpretation ID: nht72-4.28

DATE: 03/08/72

FROM: JOHN G. WOMACK FOR RICHARD B. DYSON -- NHTSA

TO: Volvo, Inc.

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your letter of February 23, 1972, in which you posed three questions concerning the test procedures of Standard 209.

Your first question concerns the passage in S5.2(j) which states that the retractor is subjected to an acceleration of 0.70 within a period of 50 milliseconds. . . . ' Your question is whether the measurement of withdrawal begins at the caset of acceleration or at the point at which an acceleration of 0.70 is achieved. Our answer is that the measurement begins at the onset of acceleration. The withdrawal that occurs within the 50 millisecond rise time will be included in determining whether the 1 inch limit has been exceeded.

Your second question concerns the sequence in which the retractor locking mechanism will be activated under S5.2(k). It is your understanding that the 10,000 locking cycles will be evenly distributed among the total 50,000 cycles. Because the standard is silent as to the sequence of testing, an even distribution is not the only test method that could be used. At the present time, the agency has one contractor who is testing in this manner and one who is testing with 40,000 cycles of extension and retraction followed by 10,000 lockup cycles. If it should prove that the latter method is more severe, however, due to the excessive wear on the same spot that you anticipated, we would (Illegible Word) to use that method and conduct our tests by evenly distributing the lockup cycles.

Your third question concerns the manner in which lockup is to be achieved during the cycling test for retractors that lock either by acceleration or by tilting. The intent of the cycling procedures is to duplicate the usage actually encountered by a retractor in a vehicle. If the retractor is sensitive to webbing withdrawal and to the acceleration of the vehicle, then the lockup mode that would be (Illegible Word) often stressed over the retractor's lifetime would be the webbing withdrawal mode and the 10,000 cycles would be cycles of lockup through webbing withdrawal. If the retractor is sensitive only to vehicle acceleration and to tilting,the most frequent cause of lockup would be vehicle acceleration and our tests will be conducted by accelerating the retractor. This is not to say that you are compiled to cycle year retractor by accelerating them. If the locking mechanism is the same for both modes (e.g. a pendulum), it may make little difference whether the retractors are accelerated or tilted. However, if our tests disclose a cycling failure, you will be obliged to show that your method was in fact equivalent to ours.