Interpretation ID: nht78-4.15
DATE: 01/06/78
FROM: AUTHOR UNAVAILABLE; J. J. Levin, Jr.; NHTSA
TO: AM General Corporation
TITLE: FMVSS INTERPRETATION
TEXT: This responds to your October 17, 1977, request for confirmation that the brake system of the M.A.N. articulated transit bus to be imported by AM General conforms to S5.1.4, S5.3.3, S5.3.4, S5.4, and S5.6.4 of Standard No. 121, Air Brake Systems. An October 17, 1977, letter from the National Highway Traffic Safety Administration (NHTSA) to Mr. Shillinger of AM General has already answered your question concerning S5.1.2.3 of the standard.
Section 108(a)(1)(A) of the National Traffic and Motor Vehicle Safety Act (the Act) (15 U.S.C. @ 1397(a)(1)(A)) requires, among other things, that no person manufacture or sell any motor vehicle manufactured on or after the date any applicable Federal motor vehicle safety standard takes effect unless it is in conformity with such standard. As the manufacturer of AM General Transit buses, I am sure you are aware that this provision makes it impossible for the NHTSA to "approve" the compliance of a brake system in advance of manufacturer of the vehicle because there can be no certainty that the vehicle as manufactured will actually comply.
In response to your statement that the bus must be tested to S5.4, @ 108(b)(2) of the Act provides that @ 108(a)(1)(A) shall not apply to any person who establishes that he did not have reason to know, in the exercise of due care, that a vehicle is not in conformity with an applicable standard. The NHTSA has always interpreted "due care" to mean that a manufacturer is free to use whatever method is reasonably calculated to assure itself that its products, if tested, would conform to the standard's requirements. Thus, dynamo-meter testing of the brakes on each bus would not be necessary if the manufacturer can, in the exercise of due care, assure itself on a reasonable basis, such as engineering calculations, that its products are capable of complying with the standard.
The NHTSA can confirm that S5.3.1 specifies that the tested vehicle be capable of stopping at least once in six stops in the specified stopping distance, within the 12-foot wide roadway, and without lockup of any wheel above 10 mph other than "controlled lockup." Section S5.3.1 specifies "no lockup" performance and can be met by any design, including one which incorporates "load sensing devices" that provide the specified performance.
Section S5.1.4 specifies "[a] pressure gauge in each service brake system . . . that indicates the service reservoir system air pressure." In the case of the M.A.N. articulated transit bus, each of the three service brake circuits must be monitored by a gauge readily visible to the driver. The agency takes no position on the wisdom of deleting pressure gauges that monitor brake chamber air pressure.
Section S5.3.3 and S5.3.4 specify minimum actuation and release times for the service brakes, measuring the time to achieve 60 p.s.i. during actuation and the time to drop from 95 p.s.i. to 5 p.s.i. during release. While these 60- and 95-p.s.i. benchmarks appear in the standard, an interpretation of them has been issued because at least one manufacturer is using a maximum air pressure that is less than the benchmarks. I enclose a copy of the clarification to answer your question.
Your question about S5.6.4 is unclear, but the NHTSA can confirm that the control lever that you showed to the NHTSA appeares to be identified in manner that specifies the method of control operation. As we understand it, the arrow suggesting clockwise rotation of the handle, in conjuction with the word "park", are intended to identify how to apply the parking brake. This interpretation only addresses an arrangement in which parking brake release is the opposite of parking brake application.
SINCERELY,
October 17, 1977 NHTSA Handling & Stability Division
Dear Mr. Perrin:
I am expressing my gratitude for your cooperation and assistance during our meeting on September 8, 1977 with Mr. Scott Shadle, M.A.N. Representatives and Westinghouse Representatives.
The following is a list by paragraph of items of FMVSS #121 discussed: S5.1.2.3 Check Valves - The use of a four-circuit protection valve in lieu of check valves as interpreted, meets the intent of the law. However, the location must be approved by NHTSA. S5.14 Gages - As interpreted, the three individual systems must have an air gage in driver's compartment.
Gages which show actual chamber pressure not required. As agreed, each of the three systems will incorporate a gage in driver's compartment and gages showing actual chamber pressure will be deleted. S5.3.3 Brake Actuation Time - As discussed, the require- ment of 0 to 60 psi in 0.45 seconds has been changed to 0 to 70% of maximum attained pressure (psi) in 0.45 seconds.
As interpreted, this will allow the use of load sensing brakes and meet the intent of the law with respect to actuation time. S5.3.4 Brake Release Time - As discussed, the release time 95-5 psig in 0.55 seconds has been changed
to maximum attainable pressure to 5 psi in 0.55 seconds.
As interpreted, this will allow the use of load sensing brakes and meet the intent of the law with respect to release time. S5.4 Service Brake System - Dynamometer Test Required to be conducted. S5.6.4 Parking Brake Control - This is related to con- figuration which will be used by Seattle-approved.
Discussion on anti-skid versus non-anti-skid:
It was pointed out that the interpretation by NHTSA that driver modulation is permissible, only one of six attempts must meet distance, 12 ft. lane and no-wheel lock up. Further, it was interpreted that load sensing brake system will meet intent of law.
I am anxiously awaiting your Department's letter indicating that the brake and air system on the Articulated Bus as discussed, to the best of your knowledge, meets the intent of FMVSS #121. However, we will ensure that certification testing is in conformance.
AM GENERAL CORPORATION
R. E. Billman Project Engineer
Attachments - 81.52100.8211 Sheet 1 81.52100.8193 Sheet 1 81.51400.8144 Sheet 3 81.99231.8779