As explained therein, "ABS is a feedback control system that attempts to maintain controlled braking under all operating conditions. (60 FR 13224).Īs background, a document that addresses the topic of antilock braking systems from the standpoint of the industry as a whole is "Antilock Brake System Review" SAE J2246 (June 1992). The opening clause of the definition states: " Antilock brake system or ABS means a portion of a service brake system that automatically controls the degree of rotational wheel slip during braking :" As noted in the preamble to the final rule adopting the definition of an ABS, the agency's definition of ABS incorporated the terms set forth in Society of Automotive Engineers (SAE) publications and European regulations to reflect the attributes of antilock systems as commonly understood by the automotive industry. (3) Transmitting those controlling signals to one or more modulators which adjust brake actuating forces in response to those signals. (2) Transmitting signals regarding the rate of wheel angular rotation to one or more controlling devices which interpret those signals and generate responsive controlling output signals and (1) Sensing the rate of angular rotation of the wheels As noted in the preamble to the final rule, for an ABS that does not require electrical power for operation, the only mandatory electrical requirement is for malfunction indicator lamps used to signal a problem in the ABS (60 FR 13227).Īn antilock brake system is defined in S4 of Standard 121 as follows:Īntilock brake system or ABS means a portion of a service brake system that automatically controls the degree of rotational wheel slip during braking by: We now turn to the terms of Standard 121.Īn ABS malfunction warning light is required by Sections 5.1.6.2 and 5.1.6.3 of Standard 121. The warning light requirements would inform operators of an ABS malfunction and both facilitate and encourage repairs of faulty ABS systems (60 FR 13244). NHTSA also determined that warning light requirements that establish a minimum level of safety are also important for reducing crashes, deaths and injuries. Because of such varying conditions, the agency determined that any ABS must be a "closed loop" system - i.e., a system that continuously monitors the rate of wheel rotation, adjusts wheel rotation when needed and reacts to ongoing changes in rotation caused by the operation of the system, by changed road surfaces, or both (60 Fed. The agency determined that due to the wide range of surfaces a vehicle may encounter in normal use, an ABS system must have the ability to determine if and when a braked wheel is momentarily locked as it passes from high to low traction conditions. One of the primary considerations in developing the new requirements was what, at a minimum, an antilock braking system must do in order to prevent or reduce crashes. In order to address the safety consequences of braking related instability, NHTSA amended FMVSS No. These crashes result in significant property damage, injury and loss of life. In the preamble to the final rule, the agency noted that 10 to 15 percent of heavy combination vehicle crashes involve braking-induced instability or loss of control. 121 were incorporated into the standard by a final rule published in the Federal Register on Ma(60 Fed. Standard 121 establishes requirements for braking systems on vehicles equipped with air brake systems. This letter supercedes our Jinterpretation.ĪBS systems and the requirements of Standard 121. NHTSA has considered these materials and additional information it has obtained. has submitted additional materials to the agency for its consideration. challenged the conclusions of our Jinterpretation, and requested further consideration. We further stated that installation of the MSQR-5000 as an ABS would not allow a vehicle to meet the requirements of Standard 121.ĪBS, Inc. Our letter to MAC trailer explained that MAC Trailer, if it manufactured a vehicle equipped with the MSQR-5000, would be responsible for ensuring that the vehicle met all applicable standards, including Standard 121. MAC Trailer, a small business manufacturing semi-trailers, asked if the MSQR-5000, manufactured by ABS, Inc., could be used to satisfy the antilock brake system (ABS) requirements of FMVSS No. an interpretation of Federal Motor Vehicle Safety Standard (FMVSS or Standard) No. James Arnold of MAC Trailer Manufacturing Inc. It is issued pursuant to orders in Air Brake Systems, Inc. 121, Air Brake Systems (49 CFR 571.121) with regard to a device sold by Air Brake Systems, Inc. This letter provides an interpretation of Federal Motor Vehicle Safety Standard (FMVSS) No. Loomis, Ewert, Parsley, Davis and Gotting
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