Interpretation ID: nht72-3.38

DATE: 09/25/72

FROM: AUTHOR UNAVAILABLE; Richard B. Dyson; NHTSA

TO: Renault, Inc.

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your letter of September 12, 1972, concerning the automatic adjustment of seat belts required by S7.1.1 of Standard No. 208.

The belt system that Renault is considering for use after August 15, 1973, employs a continuous length of webbing that runs from a floor-mounted emergency-locking retractor up through a metal ring mounted high on the B-pillar, then downward across the occupant's chest to the buckle, where it passes around a knurl bar and back across the occupant's lap to an outboard floor anchorage. Your question concerns the amount of friction that may be produced by the knurl bar before the lap belt would be considered to have lost the automatic adjustment capacity required by S7.1.1.

After examining the buckle enclosed with your letter, we have concluded that in its present (Illegible Word) the (Illegible Word) produced by the knurl bar is such that the belt would probably not adjust automatically as required by S7.1.1.

In evaluating belts of similar design, we have not attempted to quantify the amount of allowable buckle friction. The characteristic to be avoided is the tendency of the buckle to trap an excessive amount of webbing on the lap belt side of the buckle. This tendency is overcome if the friction in the buckle is low enough that the normal motion of the occupant against the shoulder belt cinches up the lap belt, or if the buckle slides down of its own weight while the assembly is stored on the B-pillar so that the next occupant must lengthen the lap belt as he fastens the buckle.

In the case of the Renault buckle, a person using the assembly after its use by a larger person would find the buckle in the position appropriate for the larger occupant. After buckling it, he would have a slack lap belt. It appears that the friction in the buckle is great enough that the occupant's normal motion would not tighten the lap belt and that he would have to adjust it manually in order to have it fit him properly. We do not consider this to be satisfactory.

If you have further questions, please advise us.