Interpretation ID: nht73-1.6
DATE: 09/11/73
FROM: AUTHOR UNAVAILABLE; L. R. Schneider; NHTSA
TO: Volkswagen of America, Inc.
TITLE: FMVSS INTERPRETATION
TEXT: This is in reply to your letter of August 8, 1973, to Mr. Schneider asking for confirmation of your interpretation of two sections of Standard No. 105a.
You ask first whether S5.3.1 requires that the activation of an indicator lamp upon application of 50 pounds of force be instantaneous, or whether a minimal time lag is permissible. You indicate that in a "panic stop" there is a time lag of approximately 100 milliseconds between application of 50 pounds of force and lamp activities in the VW system. Since, as you state, it is "humanly impossible" to discern such a minimal time lag, we consider that the VW system complies with S5.3.1, and that the lamp is activated upon application of 50 pounds of force.
You are also correct in your interpretation of S5.2.1 that the 5-minute requirement applies only to vehicles that do not exceed the limit of traction on a 30 percent grade.
Sincerely,
VOLKSWAGEN OF AMERICA, INC.
August 8, 1973
Lawrence R. Schneider -- Chief Counsel, National Highway Traffic Safety Administration
Dear Mr. Schneider:
This letter is a request for interpretation of certain language in S5.3.1 and S5.2.1 of FMVSS 105a, Hydraulic Brake Systems.
In regard to this matter a meeting was held on August 6, 1973 with personnel of the NHTSA and Volkswagen representatives. In attendance were Messrs. Taylor Vincent, E. Driver, C. Baker and V. Bloom of the NHTSA, and Messrs. G. Riechel, J. Kennebeck and K.H. Ziwica of Volkswagen of America.
1. S5.3.1 provides that "an indicator lamp shall be activated when the ignition (start) switch is in the "on" (run) position and whenever any of the following conditions occur: (a) a pressure failure in any part of the service brake system, other than a structural failure of a housing that is common to two or more subsystems, before or upon application of either (1) . . . or (2) 50 pounds of control force upon a fully manual service brake".
In the above mentioned meeting with the NHTSA, VW representatives described the conditions under which the brake failure system used by Volkswagen actuates if a failure in one of the subsystems has occurred. By using a normal or slow force application rate as shown in example "d" of attachment I, the failure indicator lamp will be activated before 50 pounds of control force are reached. By using a very fast application rate as shown in example "b" of attachment I, the indicator lamp will be activated with a certain time lag from the point where 50 pounds are reached. This characteristic is further illustrated in attachment II containing test data of a very slow control force application, and in attachment III for a panic brake force application.
In the discussion with the NHTSA representatives there was agreement that in regard to a fast control force application the wording in S5.3.1(a) "upon application of 50 pounds" does not mean that the failure indicator light must be activated instantaneously if a 50 pound control force is reached, but rather a certain time lag would be permissible before the warning light illuminates. For the panic brake situation, a time lag of approximately 100 ms, after 50 pounds control force are reached, was considered reasonable.
Based on the above mentioned discussion, we would appreciate it if you would provide us with written confirmation indicating that with a fast control force application the wording "upon application of 50 pounds" in S5.3.1(a) does not prohibit a reasonable time lag before the failure indicator lamp is activated. We want to emphasize that this interpretation would not detract from the safety intent of the requirement for failure indicators, as it is humanly impossible to discern such a minimal time lag.
2. According to S5.2.1, a parking brake system of a passenger car "shall be capable of holding the vehicle stationary (to the limit of traction of the braked wheels) for five minutes".
It is our understanding from the aforementioned discussion with the NHTSA personnel that the five minute requirement only applies to a vehicle which is able to be kept stationary by its parking brake at 30% inclination. A vehicle which slides down the 30% inclination with wheels locked by the parking brake is not required to meet the five minute requirement.
We also would appreciate receiving your written confirmation to this interpretation of S5.2.1 of FMVSS 105a.
Thank you for your cooperation in this matter.
Sincerely,
J.W. Kennebeck --
Manager,
Safety and Development
(Graphics omitted)
Attachment B
Broke Pedal applied very fast failure induced in rear circuit