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Heavy Truck Safety
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| NHTSA PROJECT ENGINEER: |
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| Updated |
Jun 3, 2004 17:43:30 |
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 124 ( -14 -11.29% ) |
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Description:
VRTC CRASH AVOIDANCE RESEARCH
Heavy Truck Research
W. Riley Garrott (rgarrott@nhtsa.dot.gov)
RESEARCH AREAS: This is an ongoing, long term VRTC research program aimed at improving the safety performance of heavy trucks. In the past, research for this program has primarily focused on braking issues, but has also included research in other heavy truck safety areas such as fuel line crossover structural integrity, tires, handling and rollover. During FY 98, testing will be completed evaluating the braking performance capability of trailers with surge brakes and electric brakes. Testing will also continue to develop ABS performance test measures for straight trucks and trailers which complement the brake-in-a-curve tests for truck tractors in FMVSS 121. Brake dynamometer fixtures from five test labs will be compared using physical measurements, two of which will also be compared using data collected from operational tests. Testing will be initiated in FY 98 to evaluate the performance improvements possible with electro-pneumatic braking systems (EBS) on heavy vehicles.
Development of ABS Performance Measures for Straight Trucks and Trailers BACKGROUND: Federal Motor Vehicle Safety Standard (FMVSS 121) requires that straight trucks and trailers built after March 1, 1998 be equipped with an antilock brake system (ABS). The standard, however, does not include performance specifications for the systems. For truck tractors, the ABS is required to allow a full treadle brake application be made on a slippery curve at a speed greater than 75 percent of the maximum speed the vehicle can be driven through the same curve.
Previous testing has indicated that this performance requirement can be extended to air-braked straight trucks. However, some additional testing is required to ensure that the performance requirement can also be extended to hydraulic-braked straight trucks.
Previous testing has shown that this performance requirement cannot be used for trailers due to the fact that the speeds attainable in the curve are significantly affected by the truck tractor used to tow the test trailer. As a result, different results are obtained depending upon the specific truck tractor used.
PLANNED RESEARCH: VRTC will borrow one air-braked and two hydraulic-braked straight trucks from manufacturers. Each vehicle will be tested to FMVSS No. 121 or No. 105, as appropriate, to ensure the respective vehicles meet Federal requirements and the brakes are burnished. They will then be run through the brake-in-a-curve performance test and the results analyzed. This data will be used to support Safety Performance Standards development of a Notice of Proposed Rulemaking (NPRM) extending this performance requirement to straight trucks. This work will be performed as quickly as possible so as to meet the Agency’s goal of issues this NPRM in 1998.
VRTC trailers will be used to evaluate various ABS system performance measures including split coefficient tests and ABS efficiency measures. These performance measures will be compared to the brake-in-a-curve method currently in FMVSS 121 for truck tractors to determine which measure results in the best test objectivity and practicality.
Evaluation of Heavy Vehicle Electro-Pneumatic Brake System (EBS) Performance BACKGROUND: The majority of current heavy vehicle brake systems use compressed air to transmit control signals from the driver to the control valves of the brake system, and to apply the brakes. While this is a relatively simple method of controlling the brake system, the time to transmit the signal can be significant and the brake system balance cannot easily be adjusted for different loading conditions. Recently, systems have been developed which would transmit the control signals electrically to control valves which then apply the brakes with compressed air. Such a system would allow for shorter transmission times, and for the possibility of dynamically refining the control strategies, with the use of various sensors, which measure vehicle performance. However, the widespread introduction of EBS cannot occur until the Agency has made changes to the appropriate FMVSS.
PLANNED RESEARCH: Four vehicle and brake system manufacturers have offered to supply vehicles for testing using their prototype EBS systems. One vehicle equipped with EBS will be borrowed from a manufacturer. A test procedure will be developed, instrumentation will be configured, and validation tests will be performed, to measure the braking performance of the EBS equipped vehicle. The resulting data will be compared with the known braking performance of conventional brake systems on similar vehicles.
One major concern about EBS is brake performance when the system has failed. An analysis will be performed with the EBS turned off, and with other simple wiring faults that are likely to occur. An in-depth analysis of more extensive EBS failure modes is beyond the scope of this pilot study. With additional funding, the three additional truck systems would be tested using the equipment and procedures developed here.
Evaluation of SAE J1802 "Brake Block Effectiveness Rating Procedures BACKGROUND: One of the prime safety features on a heavy truck is the brake system. The effectiveness rating, or how well the brake blocks provide braking torque, is a major concern for heavy truck operators. Once a truck wears out the original brake linings, nearly-exact replacements are required. The SAE J-1802 "Brake Block Effectiveness Rating" standard is an attempt to do just this. The J-1802 uses readily available, off-the-shelf, brake components, for both economy and realistic, full-scale, results. It uses a brake dynamometer for consistency and repeatability. To meet this need, several brake test laboratories are currently testing to the J-1802 specification, but are achieving large variances in their cross-correlated data. In the early 1990’s, a single fixture and brake assembly was installed and tested at the various labs, with close correlation. Large variances appeared when each laboratory ran dynamometer tests using their own fixture assemblies, set up by their own operator. Since that time, these labs have produced several variations of the J-1802 standard, and made several attempts to develop alternative standards, with little success.
PLANNED RESEARCH: The current plan is to conduct a side-by-side inspection of the five dynamometer laboratories’ "standard" fixtures. The physical dimensions of each unit will be compared to the "standard" drawings. The data will be compared to the brake simulation data developed at UMTRI if it is available before the end of this program.
Two of the fixtures will be selected for actual operational test comparison on the VRTC Greening brake dynamometer. The dynamometer tests will include two levels of agressivity of lining materials, four sets each. The linings will be mounted on cast shoes at VRTC, then cut to J-1802 specification by one of the brake test labs. Pre-conditioning of the four sets will ensure a valid cross-section of the material batch braking effectiveness. For the comparative test matrix, only two of the sets of each type of lining, will be rotated in a randomized order, between the fixtures, to minimize the effects of time and conditioning. By having the same operator set up each fixture, this will reduce the variance in the effectiveness values due to operator style.
NASA Hybrid Bus VRTC Contact: Dick Hoover |
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