Interpretation ID: nht81-1.14

DATE: 02/19/81

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: United States Testing Company

TITLE: FMVSS INTERPRETATION

TEXT:

FEB 19, 1981 Mr. Frank Pepe Assistant Vice President United States Testing Company 1415 Park Avenue Hoboken, New Jersey 07030 Dear Mr. Pepe: This responds to your recent letter concerning the requirements of Safety Standard No. 209, Seat Belt Assemblies, when applied to assemblies having dual sensitive emergency locking retractors. Your specific questions relate to the low lock-up provisions of paragraph S4.3(j) of the standard. Paragraph S4.3(j) of Safety Standard No. 209 specifies the following requirements for emergency locking retractors on seat belt assemblies: (1) Shall lock before the webbing extends 1 inch when the retractor is subjected to an acceleration of 0.7g; (2) Shall not lock, if the retractor is sensitive to webbing withdrawal, before the webbing extends 2 inches when the retractor is subjected to an acceleration of 0.3g or less; (3) Shall not lock, if the retractor is sensitive to vehicle acceleration, when the retractor is rotated in any direction to any angle of 15o or less from its orientation in the vehicle.

At the time these requirements were included in the standard, emergency locking retractors were either vehicle sensitive or webbing sensitive. Recently, however, manufacturers have been producing dual sensitive retractors that are sensitive to both vehicle acceleration and webbing acceleration. You point out that dual sensitive retractors can be tested to the requirements of S4.3(j)(3) with no problem since the webbing sensitive aspect of the retractor does not interfere. However, you state that it is impossible to isolate the vehicle sensitive portion of a dual sensitive retractor in order to test to S4.3(j)(2). Accordingly, when the retractor is accelerated to .3g under the specification of (j)(2), the vehicle sensitive portion causes the retractor to lock before 2 inches of webbing have withdrawn, even though the webbing sensitive portion of the retractor would not have caused lock-up. You explain that this occurs because most retractors containing vehicle sensitive mechanisms are designed to lock-up at low "g" force levels (i.e., a tolerance is built into the retractor to ensure that it can meet the .7g requirement of subparagraph (1)). In light of this problem, you ask whether dual sensitive retractors must comply with S4.3(j)(2).

This same question was raised by Safety Transport Inter AB, Sweden, several years ago. In an October 30, 1978, letter of interpretation responding to that question, the NHTSA Associate Administrator for Rulemaking made the following statement:

"A retractor sensitive to webbing withdrawal (even if it is also sensitive to vehicle acceleration) may properly be tested for the 0.3 g comfort requirement by holding the retractor stationary and accelerating the webbing to the required g level."

That interpretation was incorrect. Paragraph S4.3(j)(2) specifically states that the retractor is to be accelerated, not the belt webbing. Further, the agency has stated in the past that accelerating the retractor and accelerating the webbing are not equivalent tests because of inertial forces that react upon the retractor during its acceleration that are not present when the webbing alone is accelerated.

The agency believes that a dual sensitive retractor should be treated simply as either a vehicle sensitive or a webbing sensitive retractor for the purposes of the standard. The intent of the agency was to require that either vehicle sensitive or webbing sensitive retractors be used. There was no expectation that dual sensitive retractors would be used and no intent that a retractor be required to meet the requirements for both types of retractors. The provision of webbing sensitivity in a retractor that meets the vehicle sensitivity requirements is a voluntary act and therefore is not subject to the standard. Likewise, the provision of vehicle sensitivity in a retractor that meets the webbing sensitive requirements is a voluntary act.

This approach will resolve the conflict that has arisen with the compliance envelopes established in S4.3(j)(1) and (j)(2), given the compliance tolerances which manufacturers are designing into newer retractors. Since vehicle sensitive mechanisms are being designed so that they activate before the .7g's required in (j)(1) is reached, the retractor locks before the webbing sensitive portion of the retractor is activated. Therefore, these dual sensitive retractors can not be tested for compliance with (j)(2).

Under this approach, a manufacturer wishing to treat its dual sensitive retractor as a vehicle sensitive retractor for the purposes of Standard No. 209 would have to comply with S4.3(j)(1) and (3). A manufacturer wishing to treat its dual sensitive retractor as a webbing sensitive retractor would have to comply with S4.3(j)(1) and (2).

I hope this has been responsive to your inquiry. If you have any further questions, please contact Hugh Oates of my office (202-426-2992).

Sincerely,

Frank Berndt Chief Counsel

October 15, 1980

Mr. Frank Berndt Chief Counsel National Highway Traffic Safety Administration 400 - 7th Street Washington, D.C. 20590

RE: FMVSS No. 209 Seat Belt Assemblies Interpretation, Emergency Locking Retractor, Lock-Up Requirement

Dear Mr. Berndt:

Some questions have been raised pertaining to the requirements for Dual Sensitive Emergency Locking Retractors when tested in accordance with FMVSS No. 209. The questions pertain to the low lock-up requirements (0.3g) Paragraph S4.3 (j).

A dual-sensitive retractor is a combination of webbing sensitive and vehicle sensitive locking mechanisms. The specifications clearly states requirements for either one of the mechanisms but does not take into account the combination of both in the same retractor. Consequently, an interpretation is needed to clarify the requirements of this type of retractor.

Our interpretation of the Standard, Para. S4.3 (j) (1) (2) and (3) as it applies to a dual-sensitive retractor is as follows:

(1) Shall lock before the webbing extends one (1) inch when the retractor is subjected to an acceleration of 0.7 g.

Comment: Applies to all types of emergency locking retractors

(2) Shall not lock, if the retractor is sensitive to webbing withdrawal, before the webbing extends two (2) inches when the retractor is subjected to an acceleration of 0.3 g or less.

Comment: Applies only to webbing sensitive type retractors. In dual sensitive retractors there is no way of isolating the vehicle sensitive portion (without disturbing an integral part of the retractor mechanism) to check the webbing sensitivity portion at 0.3 g. There is no requirement at 0.3 g for a strictly vehicle sensitive retractor. It should also be noted that most retractors containing vehicle sensitive mechanisms are designed to lock-up at low g force levels. This is to insure user confidence in the assembly during low level loading, such as braking.

(3) Shall not lock, if the retractor is sensitive to vehicle acceleration, when the retractor is rotated in any direction to any angle of 15o or less from its orientation in the vehicle.

Comment: Applies to both vehicle sensitive and dual-sensitive retractors.

I would appreciate your prompt review of the above interpretation and any comments you may have pertaining to same.

Very truly yours,

Frank Pepe Assistant Vice President Engineering Division

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