Interpretation ID: nht95-4.79

TYPE: INTERPRETATION-NHTSA

DATE: November 16, 1995

FROM: Dietmar K. Haenchen -- Manager, Vehicle Regulations, Volkswagen of America, Inc.

TO: Chief Counsel -- NHTSA

TITLE: Request for Interpretation, FMVSS 124 "Accelerator Control Systems"

ATTACHMT: 1/19/96 letter from Samuel J. Dubbin to Dietmar K. Haenchen (A44; Std. 124)

TEXT: This letter is to request an interpretation with regard to the provisions of Section S5.1 which requires "at least two sources of energy capable of returning the throttle to the idle position within the time limits specified by S5.3 . . . In the event of failure of one source of energy by single severance or disconnection, the throttle shall return to the idle position within the time limit specified by S5.3 . . ."

The specific question for interpretation relates to the compliance under S5.1 of a system using a coil spring composed of multiple strands of wire twisted into a wire cable which is then coiled into a spring. This would provide "at least two sources of energy" because the individual strands that compose the wire cable each provide a separate source of energy. A drawing of such a spring showing a cable of three strands of wire is attached. Also enclosed is a sample spring which uses seven strands of w ire. Assuming in the spring consisting of three strands of wire, that if only one strand is broken, the remaining two would have sufficient force to return the throttle to idle, we believe such a spring would comply with S5.1 of the Standard. The seven strand wire spring provides even greater redundancy if, for example, the spring would have sufficient force to return the throttle to idle if up to three of the wire strands were broken. Endurance testing on seven strand wire springs without damage and with intentional damage has shown that even if damaged by the separation of one or two wire strands, the coil spring is still fully functional with enough torque to perform its intended function.

For purposes of this request for interpretation, it should be assumed that only a single coil spring consisting of the multiple strands would be provided to close the throttle.

Your response as soon as possible (within 30 days) will be appreciated.

Drawing omitted.