This dissertation details the methods and analysis of extensive physical tests and simulation conducted by the Center for Vehicle Systems and Safety (CVeSS) at Virginia Tech on the maneuverability, roll-stability, and brake type performance of 33-ft double trailers. Little literature exists for 33-ft doubles because they are uncommon on the U.S. roads due to current federal restrictions limiting long-combination vehicles to 28-ft doubles. With the continual rise in e-commerce, however, there is a push by package carriers on legislation to permit carriers to introduce 33-ft doubles into their fleets. Three separate studies detailed herein highlight 33-ft double trailers' off-tracking, roll-stability with stability control systems, and brake type influence on braking performance.
The first study compares low-speed off-tracking of a 33-ft double to 28-ft double and 53-ft single configurations via simulation and full-scale tests. Novel numerical tractrix models are introduced and compared to existing models commonly used to evaluate low-speed off-tracking of long combination vehicles (LCVs). Unlike pre-existing models, accuracy of one of the proposed models is largely unaffected by input path resolution and regularity—a significant benefit for reducing computational cost and easing implementation for many applications. Full-scale tests are conducted at Virginia Tech and an extensive uncertainty analysis is detailed for the test procedure and measurements. Field tests compare favorably with simulations for all tested maneuvers and trailer configurations and clearly demonstrate the order from least to most off-tracking as 28-ft double, 33-ft double, and 53-ft single. The 33-ft doubles have slightly larger off-tracking than 28-ft doubles, whereas 53-ft singles have substantially larger off-tracking than 28-ft and 33-ft doubles.
The second study evaluates 33-ft double straight-rail trailers rollover propensity with different stability control system implementations: stock (none), tractor electronic stability control (ESC), trailer roll-stability control (RSC), and RSC+ESC. Extensive test vehicle instrumentation and structural reinforcement are detailed for the test preparations. Tests are conducted on a test track with either driver or robot steering. On their own, both ESC and RSC clearly reduce the rollover propensity of the trailers for all maneuvers, and the trailers exhibit the highest roll-stability when both RSC and ESC are active. The tested ESC and RSC modules are off-the-shelf products from industry suppliers chosen by the program sponsor.
The third study compares trailer drum and disc brake performance in three conditions: straight-line braking distance, brake type influence on RSC performance, and roll dynamics in a combined braking and turning maneuver. A braking robot is designed, fabricated, and implemented to provide precise and repeatable brake pedal application. Test results suggest that disc brakes tend to provide reduced braking distance and are less susceptible to brake fade than drum brakes. Anti-lock braking system (ABS) and suspension dynamics react differently to the two brake types. Small, noticeable differences in RSC performance are evident between the two brake types. Within the test limitations, rollover dynamics were not clearly different between the two brake types for braking-in-turn maneuvers, performed for a large range of entry speeds and brake activation delay relative to the start of steering. / Doctor of Philosophy / Due to their large size, mass, and high center-of-gravity, heavy vehicles, especially long combination vehicles (LCVs) require a substantial amount of space to negotiate turns, long distances to brake from highway speeds to a stop and are susceptible to rollover. Combination vehicles on the U.S. roads are commonly in 53-ft single trailer or 28-ft double trailer configurations. With the continual rise of e-commerce, package carriers are pursuing 33-ft double trailers to increase each vehicle's cargo volume. Before introducing these trailers into a fleet, there is a need to understand (1) if 33-ft doubles can negotiate existing routes traveled by 28-ft double and 53-ft single configurations, (2) if 33-ft doubles can benefit from existing stability control systems, and (3) how trailer brake types perform on 33-ft doubles. Three separate studies are conducted to address these topics. The first study compares off-tracking for the three mentioned trailer configurations through low-speed, real-world maneuvers via physical full-scale tests and simulation. Off-tracking is a metric illustrative of maneuverability and is defined as the relative distance in paths of the rearmost axle to the lead steer axle. New mathematical models are introduced and used to simulate vehicle motion through low-speed maneuvers. The simulation and field tests determine that, for all tested maneuvers, the order from smallest to largest off-tracking is 28-ft double, 33-ft double, and 53-ft single configurations, with the 33-ft doubles having slightly larger off-tracking than 28-ft doubles. This suggests that 33-ft doubles can travel through routes typically traveled by a 53-ft single but need slightly more space on the road than a 28-ft double. The second study tests 33-ft double trailers with and without stability control systems. Tests, conducted at a test track, are designed to replicate real-world maneuvers that induce trailer rollover. It is found that the 33-ft double trailers are clearly less likely to rollover with the tested stability enhancement systems than without. The tests also illustrate that the different tested control systems' effectiveness in reducing rollover propensity is maneuver dependent. The third study tests the braking distance, brake influence on the stability control systems, and rollover dynamics while braking-in-turn for two different types of brakes, drum brakes and disc brakes. Small but evident differences in the performance of the two brake types suggest disc brakes could provide shorter stopping distance and time at highway speeds, compared with drum brakes. The studies detailed in this dissertation provide valuable information on 33-ft doubles dynamics and provide guidance for their safe introduction on the U.S. roadways.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/111432 |
| Date | 02 August 2022 |
| Creators | Neighborgall, Campbell Reed |
| Contributors | Mechanical Engineering, Ahmadian, Mehdi, Akbari Hamed, Kaveh, Taheri, Saied, Southward, Steve C., Stilwell, Daniel J. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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