TECOM PROJECT NO. 1-VG-505-CBI-001
REPORT NO. ATC-8260
CONSUMER BRAKING INFORMATION
INITIATIVE - PHASE II
STEVEN E. KING
AUTOMOTIVE INSTRUMENTATION TEAM
U.S. ARMY ABERDEEN TEST CENTER
ABERDEEN PROVING GROUND, MD 21005-5059
U.S. ARMY DEVELOPMENTAL TEST COMMAND
DISTRIBUTION LIMITED TO U.S. GOVERNMENT
Consumer Braking Information
Final Report for the Methodology Study of the Consumer Braking Information Initiative - Phase II
Work Performed by U.S. Army Aberdeen Test Center, Fall 1999
Note: the following report is also available for viewing on the Department of Transportation docket website. Go to http://dms/search and use Docket No. 6583.
NHTSA is investigating the feasibility of developing a braking performance measurement test procedure for light vehicles. The development of a suitable test procedure to evaluate the braking performance of light vehicles would enable NHTSA to provide braking performance information such as stopping distance, in addition to crash test performance information, as part of the agency's New Car Assessment Program (NCAP), on those new vehicles that are purchased for use in crash tests under the NCAP.
In Phase I of this program, the Aberdeen Test Center, a division of the U.S. Army Material Command, in Aberdeen Maryland, developed a preliminary test procedure and investigated the variability in stopping distance tests on ten light vehicles, using a straight-line braking maneuver from 62 mph (100 km/h), on both wet and dry pavement. In this report on Phase II of the Aberdeen program, round-robin testing of four light vehicles was performed at three different test facilities to determine the variability associated with using different test tracks and test drivers.
The four vehicles tested were a mid-size passenger car, a mini-van, a mid-size sport utility vehicle, and a full-size pickup truck. All were 1999 model year vehicles that were leased with mileage accumulations ranging from 9,000 to 17,000 miles. The vehicles were prepared by installing all new foundation brake components (linings, rotors, drums, and brake hardware) purchased from the original equipment manufacturer, installing new tires as the vehicle was originally equipped, and then conducting a brake burnish to wear-in the new brakes according to the burnish procedure in Federal Motor Vehicle Safety Standard No. 135. The vehicles were instrumented with thermocouples to measure front brake lining temperatures. A fifth wheel was used to measure stopping distance, and brake pedal force was measured with a pedal force transducer. Brake pedal force indications were provided to the test driver through a series of lamps mounted on top of the instrument panel that activated at pre-set pedal forces, and the beginning of each stop was triggered using the vehicle's stop lamp circuit. Aberdeen supplied the data acquisition systems.
As was the case in Phase I, all of the vehicles were equipped with four-wheel antilock braking systems (ABS). By using only ABS-equipped vehicles, the driver is able to make a rapid, hard brake pedal application resulting in the ABS controlling the brake forces at the wheels to prevent wheel lockup and provide minimal stopping distance. The vehicles were to be loaded to an equivalent weight of approximately two passengers, or 400 lbs., although in this program test weights were slightly higher than this target. The test weight consisted of the test driver, data acquisition system installed on the rear seat, and a water ballast tank installed on the front passenger's seat.
Four rounds of testing were conducted at three test facilities, including Abderdeen, MGA Research in Madison Wisconsin, and the Transportation Research Center (TRC) in East Liberty Ohio. The first and fourth rounds of testing were both conducted at Aberdeen. Pavement friction was measured at each facility using a skid trailer, and meteorological measurements including air and road surface temperature and wind speed were monitored during the testing. Test surface slope and grade measurements were recorded.
The peak friction coefficient (PFC) measurements performed at Aberdeen indicated that during the first round of testing, the dry PFC was 0.94 and the wet PFC was 0.93.PFC measurements during the fourth round of testing at Aberdeen were higher for the dry pavement, at 0.95 and 1.00 for pre- and post-test measurements, respectively.PFC measurements of the wet pavement at Aberdeen for the fourth round were 0.91 and 0.90 for pre- and post-test measurements, respectively.The increase in dry PFC from the first to the fourth round resulted in shorter stopping distances ranging from two to ten feet, on both wet and dry pavement, for the four vehicles tested.
The PFC measurements from TRC for dry pavement were 0.91 and 0.94 for pre- and post-test measurements, respectively, and for wet pavement were 0.84 and 0.83 for pre- and post-test, respectively. The difference in PFC between Aberdeen (higher PFC) and TRC (lower PFC) resulted in stopping distances of 6 to15 feet longer at TRC than the fourth round Aberdeen stopping distances. The PFC measurements at MGA were 0.99 and 0.95 for pre- and post-test dry pavement, respectively, and 0.97 and 0.96 for pre-and post-test wet pavement, respectively.The MGA test surface had several pavement repair strips, which affected the vehicle stopping results with larger standard deviations for each series of stops on each vehicle, compared to the results from Aberdeen and TRC.
The test drivers were provided by each test facility to determine if different drivers could consistently attain rapid brake pedal applications.A target pedal of 100 lbs. within 0.1 seconds of activation of the vehicle's stop lamp circuit was used as in the Phase I effort, with each driver instructed to target 150 lbs. of brake pedal force thereafter.Only the TRC driver was able to consistently achieve 100 lbs. of pedal force in 0.1 seconds. Results comparing various brake pedal application rates showed that in some cases, brake pedal application rates slower than 100 lbs. in 0.2 seconds resulted in longer stopping distances and/or increased standard deviation.It was also found that in order to achieve rapid brake application, as the TRC driver did, that the 150 lbs. pedal force target would be exceeded, with pedal forces peaking at approximately 250 lbs. momentarily. However, high brake pedal forces were not found to have an effect on stopping distance results.
As with the Phase I report, NHTSA does not intend this report to provide comparative stopping distance information for the vehicles tested.Rather, the research is part of a continuing effort to develop a test protocol that could be used to measure the braking performance of NCAP vehicles.The results of this Phase II testing indicate that using a test driver to perform stopping distance tests is practical when vehicles are equipped with 4-wheel ABS.Controlling the test surface will be of primary importance since it does affect stopping distance results.
TABLE OF CONTENTS
SECTION 1. BACKGROUND, OBJECTIVES, AND TASKS
|III||TASK 1 - OBTAIN AND PREPARE TEST VEHICLES|
|IV||TASK 2 - PREPARE FACILITIES AND TEST EQUIPMENT|
|V||TASK 3 - BRAKE BURNISH|
|VI||TASK 4 - STOPPING DISTANCE TESTS|
|VII||TASK 5 - ENVIRONMENTAL MEASUREMENTS|
|VIII||TASK 6 - SECOND ROUND OF TESTING|
|IX||TASK 7 - THIRD ROUND OF TESTING|
|X||TASK 8 - FOURTH ROUND OF TESTING|
|XI||TASK 9 - DATA ANALYSIS AND REPORTING|
SECTION 2. APPENDIXES
|B||REPLACEMENT PARTS LISTING|
|C||VEHICLE INSTRUMENTATION PHOTOGRAPHS|
|D||TEST SITE PHOTOGRAPHS|
|E||FIRST ROUND TEST DATA|
|F||SECOND ROUND TEST DATA|
|G||THIRD ROUND TEST DATA|
|H||FOURTH ROUND TEST DATA|
|I||BRAKE PEDAL EFFORT COMPARISON|
|J||WIND EFFECTS ANALYSIS|
|K||GRADE EFFECTS ANALYSIS|