Interpretation ID: nht75-6.16

DATE: 06/13/75

FROM: AUTHOR UNAVAILABLE; James B. Gregory; NHTSA

TO: S.L. Terry, Vice President

TITLE: FMVSS INTERPRETATION

TEXT:

S. L. Terry, Vice President Public Responsibility and Consumer Affairs Chrysler Corporation P. O. Box 1910 Detroit, MI 48231

Dear Mr. Terry:

This responds to your letter of May 13, 1975, requesting confirmation that Chrysler's new unibelt shoulder/lap belt system with a "window shade" tension adjustment feature satisfies the requirements of S7.1.1 of Standard No. 208, Occupant Crash Protection, that the lap belt portion "adjust by means of an emergency-locking or automatic-locking retractor." You describe the seat belt assembly as of the single retractor, continuous loop type, with a B-pillar-mounted "window shade" emergency-locking retractor, and a one-way locking device in the buckle tip which prevents return of webbing to the lap portion from the torso portion when the belt assembly is in use.

Section 7.1.1 requires adjustment of the lap belt portion "by means of an emergency-locking or automatic-locking retractor" and adjustment in most cases of the upper torso portion "by means of an emergency-locking retractor." The language permits some single retractor, continuous loop systems as long as the single retractor does "automatically adjust" the tension of the lap bolt portion to prevent excessive slack. Because of the submarining danger of a slack lap belt, the National Highway Traffic Safety Administration (NHTSA) has restricted the acceptability of continuous loop systems under S7.1.1 in two areas.

One restriction, set forth in a letter to Renault, Inc., on September 25, 1972, is that "the friction in the buckle is low enough that the normal motion of the occupant against the shoulder bolt cinches up the lap belt."

We would like to clarify that letter by emphasizing that, to conform to the requirements, the assembly must be designed by the manufacturer with a sufficiently low level of friction to qualify the lap portion as automatically adjustable." Thus, it is the manufacturer who determines whether or not the particular bolt system is designed to satisfy the requirements of the standard. In your May 16, 1975, demonstration to Messrs. Hitchcock, Nelson, Medlin, Smith, Breedon, and Ziegler of the NHTSA, we saw no evidence of design deficiency in limited use of that continuous loop system.

The other restriction was set out in a March 9, 1973, letter to General Motors. It limits the use of "comfort clips" on the upper torso portion of continuous loop systems. The letter distinguishes continuous loop systems from systems that have separate lap and shoulder belt retractors. It concludes that "a comfort clip would be acceptable under S7.1.1 of the standard, so long as the shoulder belt is otherwise capable of adjustment as required by S7.1.1."

This restriction has since been the subject of an NHTSA proposal (Docket No. 74-32, Notice 1) which would restrict the use of "a device used to limit retractive action of an emergency-locking retractor for the comfort of the occupant" to seat belt assemblies that have "an individually adjustable lap belt." Chrysler's response to that proposal and stated plan to introduce a continuous loop belt system with a "window shade" device in the new 1976 model four-door compact car assume that NHTSA intends to permit "belt tension relief" devices on all continuous loop systems. I would like to point out that this issue is still outstanding in Docket No. 74-32.

Sincerely,

(original stamped by)

James B. Gregory Administrator

May 13, 1975

Dr. James B. Gregory Administrator National Highway Traffic Safety Administration 400 Seventh Street, S.W. Washington, DC 20591

Dear Dr. Gregory:

Chrysler Corporation plans to introduce a new unibelt shoulder/lap belt system with a "window shade" tension adjustment feature for the front seat outboard seating positions during the 1976 model year. We plan to introduce this system initially in the 4-door models of our all-new compact car, and later in the model year incorporate the system in all of our other 1976 model 4-door cars, including station wagons. As indicated in my letter dated November 7, 1974 (commenting on Docket 74-32, Notice 1, based on discussions with the Administration), we understand that a unibelt system with a "window shade" adjustment feature will conform to current MVSS 208 requirements provided it otherwise complies with MVSS 209. Because the modifications to proposed Docket 74-32 are still pending and we have not yet received written confirmation of our understanding, we hereby request that the Administration review our unibelt system and provide us with written response indicating that it complies with the regulations. Since we must make commitments for final tooling almost immediately, we request your review as soon as possible.

The system consists of a continuous webbing loop with a vehicle deceleration sensitive emergency-locking retractor located in the B-pillar. The webbing is routed from the retractor to a roof rail mounted turning loop, across the occupant's upper torso to the buckle tip, across his lap and down to the floor anchor. To encourage belt usage by making them more comfortable to wear, we have incorporated a "window shade" feature in the retractor to relieve objectionable shoulder belt tension. A slight extension of the shoulder belt provides slack in the shoulder belt; a second extension of the belt releases the slack.

To maintain lap tension when shoulder belt tension has been relieved by using the "window shade" in the retractor, we have incorporated a one-way locking device in the buckle tip. This permits the belt webbing to be pulled through the buckle tip by the retractor, but prevents webbing movement in the opposite direction. It also permits the user to tighten the lap belt beyond the tension created by the retractor, if he likes a snug lap belt.

We believe that this system is a significant step forward in the design of seat belt systems. Initially, it makes the belt buckle tip easier to find since it normally stows near the roof rail rather than near the floor between the door and seat. It is easier to buckle up because the motion required by the occupant to extend the webbing from the single retractor is more nearly linear. After buckling up, the occupant can easily relieve shoulder belt tension by moving forward slightly and then returning to his normal sitting position. If the occupant wishes, greater tension can be placed and maintained in the lap belt by pulling the shoulder belt upward. Moreover, this system is automatically and conveniently stored by tripping the "window shade." It also eliminates the lap belt cinch- up problem associated with auto-locking retractors which many customers find objectionable. Because this new design will encourage the use of seat belts and as we are able to work out the problems of application of the system of other car models, we expect to offer this system on our 2-door models.

Based on our interpretation of the requirements of MVSS 208 and MVSS 209, and our understanding of the letters of interpretation issued by the NHTSA to Renault dated September 25, 1972, and to General Motors dated March 27, 1975, we believe our new system fully complies with the applicable requirements of both standards. With respect to the issue raised in those letters, we have designed the one-way lock-up feature in the buckle tip of our system to allow self-adjustment of the lap belt by the retractor. When the occupant does not snug the lap belt, our testing experience indicates that normal occupant motions will cause the slack in the system to be taken up by the retractor.

Based upon this description of our new unibelt lap/shoulder belt system that we plan to use during the 1976 model year, we request a letter of confirmation of our interpretation that this system complies with the requirements of the Federal Motor Vehicle Safety Standards. If considered desirable, we would be happy to demonstrate this new system in one of our vehicles.

Very truly yours,

CHRYSLER CORPORATION

(original signed by)

S. L. Terry Vice President Public Responsibility and Consumer Affairs

/ms