Interpretation ID: nht93-4.4
DATE: May 19, 1993
FROM: Richard A. Zander -- Project Engineer, AlliedSignal Automotive Proving Grounds
TO: Office of Chief Council, NHTSA
TITLE: None
ATTACHMT: Attached to letter dated 3/23/94 from John Womack to Richard A. Zander (A42; Std. 105)
TEXT:
I am writing to obtain your official interpretation of the following statement in 49 CFR 57, 105 Section S5.1.4.2(a) "each vehicle with GVWR of 10,000 lbs. or less shall be capable of making 5 fade stops (10 fade stops on the second test) from 60 mph at a deceleration not lower than 15 fpsps for each stop, followed by 5 fade stops at the maximum deceleration attainable from 5 to 15 fpsps."
I am requesting your official interpretation of the phrase "at a deceleration not lower than 15 fpsps for each stop." As further reference Section S7.11.2.1 states "Attain the required deceleration within 1 second and, as a minimum, maintain it for the remainder of the stopping time."
Within the industry, I know of three different interpretations of this statement, there could by more:
1. The average deceleration for the stop must be greater than 15 fpsps. The average deceleration is calculated from one second after the stop begins to a vehicle speed of 5 mph.
2. After 1 second the deceleration can not drop below 15 fpsps even for an instant. If the deceleration drops below 15 fpsps at any time it is considered a failure even if the average deceleration is greater than 15 fpsps. 3. The average deceleration for the stop must be greater than 15 fpsps and the deceleration must be greater than 15 fpsps for at least 75% of the stop excluding the first second of the stop.
In the "Laboratory procedures for FMVSS No. 105-83, TP-105-83-00, dated January 31, 1984, page 1.49, data sheet No. 1.16 for the fade stops, requests the following information for the deceleration "Average Sust Decel" see pages 1 and 2 of Attachment A. Therefore, it appears that NHTSA's interpretation of the statement "at a deceleration not lower than 15 fpsps for each stop" is "the average sustained deceleration."
Pages 3 & 4 of attachment A are a typical fade stops. The X axis is time and on the Y axis is deceleration and pedal force.
Interpretation ONE would consider these a pass because the average deceleration was greater than 15 fpsps and the pedal force did not exceed 150 lbs.
Interpretation TWO would consider these a fail because several data points fell below 15 fpsps. This interpretation appears to not consider the intent of the fade procedure. The intent being that a vehicle be capable of making multiple
high deceleration stops in a short period of time without drastic changes in effectiveness. Thus the recovery stops have a maximum and a minimum pedal force requirement based on the baseline check stops.
Maintaining an average deceleration of at least 15 fpsps insures adequate heat build up in the linings to determine if they will fade or drastically change effectiveness.
The deceleration could fall below 15 fpsps for short periods of time due to instrumentation noise or in stop fade which was not immediately compensated for by the driver. Interpretation THREE would consider these a pass because the average deceleration is greater than 15 fpsps and the deceleration is greater than 15 fpsps for 75% of the stop after the first one second.
Considering the intent of the fade procedure, the 75% requirement is not necessary to insure adequate heat build-up in the linings.
The NHTSA interpretation "average sustained deceleration" would also consider these a pass.
I am also requesting that you send the latest version of the test procedure for FMVSS No. 105 from the office of vehicle compliance. Please send to:
Richard Z. Zander Allied Signal Automotive Proving Grounds 3214 State Road 2 New Carlisle, IN 46552
Thank you for your time and effort to respond to my requests.
ATTACHMENT
Laboratory Procedures for Federal Motor Vehicle Safety Standard No. 105-83; TP-105-83-00; January 31, 1984. (Text omitted)