Rearward Amplification Suppression (RAMS)

008109592000Final Report April 15, 1999-September 15, 2000PDFTech ReportUMTRI-2000-47DTFH61-96-C-00038AlgorithmsAutomatic brakingControl systemsOscillationRollover crashesTrailer swingTractor trailer combinationsTrailersDynamic brakingBrakingHighwaysMotor CarriersSafety and Human FactorsVehicles and EquipmentI91: Vehicle Design and SafetyUnited StatesWashington (District of Columbia)United States. Federal Highway AdministrationMacAdam, C.Hagan, MichaelFancher, PaulWinkler, C.Ervin, RobertZhou, JamesBogard, S.University of Michigan. Transportation Research InstituteUnited States. Federal Highway AdministrationUS Transportation CollectionThe basic goal of this work was to develop and demonstrate an automatic brake control system that could intervene -- only when needed -- to help suppress unwanted trailer oscillations (commonly referred to as rearward amplification) in large combination vehicles (typically double and triple trailer combinations). The system would only be enabled for highway speed conditions greater than 50 mph. If possible, the system would be so simple that it could be provided on a trailer-by-trailer basis. That is, the proposed system, when implemented on a particular trailer within a combination vehicle train, would not have to depend upon sensor information from units ahead of it or behind it in order to function properly and yet provide significant benefit. The primary focus therefore of this work was on the development and demonstration of a so-called "trailer-only" RAMS (Rearward Amplification Suppression) system. Another aspect of this work was the perceived need to "keep it simple," thereby facilitating the implementation and potential adoption of a RAMS functionality (and its associated vehicle outfitting) by the truck and trailer user community. Thus the emphasis here on a "trailer-only" system. Further, if the outcome of this study was successful at demonstrating the effectiveness of a practical and simple-to-implement RAMS system, then it was deemed likely that a follow-on field trial of the proposed system could be executed by a third party subsystem manufacturer (perhaps in partnership with the U.S. Department of Transportation) to evaluate the RAMS system in actual practice. Key findings from the work include: A particular "Trailer-Only RAMS System" has been developed and shown to be highly effective at reducing rearward amplification in double and triple trailer combinations on both dry and wet high friction surfaces. None of the RAMS systems examined within the study was seen to provide directional stability benefits on very low friction surfaces (e.g., wet jennite, ice/snow, etc.). A "safe harbor" -- in terms of rearward amplification tendencies -- exists for most combination vehicles at speeds below 45 mph. Consequently, the speed reduction that accompanies a RAMS intervention provides a beneficial byproduct of increased directional damping to the vehicle as it slows down.81