Center for Vehicle Systems and Safety (CVeSS)

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https://hdl.handle.net/10919/52017

The Center for Vehicle Systems and Safety (CVeSS) at Virginia Tech was established in 2004 by Dr. Mehdi Ahmadian, professor of Mechanical Engineering, and director of CVeSS. The center consists of four laboratories: The Advanced Vehicle Dynamics Laboratory (AVDL, established 1995), Vehicle Terrain Performance Laboratory (VTPL, established 2006), Performance Engineering and Research Laboratory (PERL, established 2006) and Railway Technologies Laboratory (RTL, established 2004). The center is served by five full-time faculty, more than twenty graduate students, a large number of undergraduate students and technical personnel. Several other Virginia Tech faculty members and visiting scholars are CVeSS affiliate faculty.

Through its affiliated labs, CVeSS is engaged in a wide variety of research ranging from advanced vehicle suspensions, to measurement and modeling of terrain and terramechanics, to biodynamics, to dynamic control of vehicle systems, to vehicle stability and rollover anlysis. The research at CVeSS is broad. It encompasses a myriad of analytical, modeling, and experimental work. We work closely with our sponsors to come up with ways and methods of improving their existing and future products, improve their market share, and ultimately bring added value to their services and products.

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A Review on Eigenstructure Assignment Methods and Orthogonal Eigenstructure Control of Structural Vibrations
Rastgaar, Mohammad; Ahmadian, Mehdi; Southward, Steve (Hindawi, 2009-01-01)
This paper provides a state-of-the-art review of eigenstructure assignment methods for vibration cancellation. Eigenstructure assignment techniques have been widely used during the past three decades for vibration suppression in structures, especially in large space structures. These methods work similar to mode localization in which global vibrations are managed such that they remain localized within the structure. Such localization would help reducing vibrations more effectively than other methods of vibration cancellation, by virtue of confining the vibrations close to the source of disturbance. The common objective of different methods of eigenstructure assignment is to provide controller design freedom beyond pole placement, and define appropriate shapes for the eigenvectors of the systems. These methods; however, offer a large and complex design space of options that can often overwhelm the control designer. Recent developments in orthogonal eigenstructure control offers a significant simplification of the design task while allowing some experience-based design freedom. The majority of the papers from the past three decades in structural vibration cancellation using eigenstructure assignment methods are reviewed, along with recent studies that introduce new developments in eigenstructure assignment techniques.
Nonlinear vibrations of microcantilevers subjected to tip-sample interactions: Theory and experiment
Delnavaz, Aidin; Mahmoodi, S. Nima; Jalili, Nader; Ahmadian, Mehdi; Zohoor, Hassan (American Institute of Physics, 2009-12-01)
Improvement of microcantilever-based sensors and actuators chiefly depends on their modeling accuracy. Atomic force microscopy (AFM) is the most widespread application of microcantilever beam as a sensor, which is usually influenced by the tip-sample interaction force. Along this line of reasoning, vibration of AFM microcantilever probe is analyzed in this paper, along with analytical and experimental investigation of the influence of the sample interaction force on the microcantilever vibration. Nonlinear integropartial equation of microcantilever vibration subject to the tip-sample interaction is then derived and multiple time scales method is utilized to estimate the tip amplitude while it is vibrating near the sample. A set of experiments is performed using a commercial AFM for both resonance and nonresonance modes, and the results are compared with the theoretical results. Hysteresis, instability and amplitude drop can be identified in the experimental curves inside the particle attraction domain. They are likely related to the interaction force between the tip and sample as well as the ever-present water layer during the experiments. A fair agreement is observed between the theoretical simulations and experimental findings, which obviously demonstrates the effectiveness and applicability of the developed model.
An SMA Passive Ankle Foot Orthosis: Design, Modeling, and Experimental Evaluation
Deberg, Liberty; Taheri Andani, Masood; Hosseinipour, Milad; Elahinia, Mohammad (Hindawi, 2014-06-02)
Shape memory alloys (SMAs) provide compact and effective actuation for avariety of mechanical systems. In this work, the distinguished superelastic behavior of these materials is utilized to develop a passive ankle foot orthosis to address the drop foot disability. Design, modeling, and experimental evaluation of an SMA orthosis employed in an ankle foot orthosis (AFO) are presented in this paper. To evaluate the improvements achieved with this new device, a prototype is fabricated and motion analysis is performed on a drop foot patient. Results are presented to demonstrate the performance of the proposed orthosis.
A Novel Double-Piston Magnetorheological Damper for Space Truss Structures Vibration Suppression
Wang, Qiang; Ahmadian, Mehdi; Chen, Zhaobo (Hindawi, 2014-07-22)
The design, fabrication, and testing of a new double-piston MR damper for space applications are discussed. The design concept for the damper is described in detail. The electromagnetic analysis of the design and the fabrication of the MR damper are also presented. The design analysis shows that the damper meets the weight and size requirements for being included in a space truss structure. The prototype design is tested in a damper dynamometer. The test results show that the damper can provide nearly 80 N of damping force at its maximum velocity and current. The test results also show that the seal drag could contribute significantly to the damping forces. Additionally, the test results indicate that both the work by the damper and damping force increase rapidly with increasing current at lower currents and taper off at higher currents as the damper starts to saturate. The damper force versus velocity plots show hysteresis in both pre- and postyield regions and asymmetric forces in jounce and rebound. A model is proposed for representing the force-displacement, force-velocity, and asymmetric forces observed in test results. A comparison of the modeling results and test data indicates that the model accurately represents the force characteristics of the damper.
Pneumatically Balanced Heavy Truck Air Suspensions for Improved Roll Stability
Chen, Yang; Ahmadian, Mehdi; Peterson, Andrew (SAE International, 2015-01-01)
This study provides a simulation evaluation of the effect of maintaining balanced airflow, both statically and dynamically, in heavy truck air suspensions on vehicle roll stability. The model includes a multi-domain evaluation of the truck multi-body dynamics combined with detailed pneumatic dynamics of drive-axle air suspensions. The analysis is performed based on a detailed model of the suspension's pneumatics, from the main reservoir to the airsprings, of a new generation of air suspensions with two leveling valves and air hoses and fittings that are intended to increase the dynamic bandwidth of the pneumatic suspensions. The suspension pneumatics are designed such that they are able to better respond to body motion in real time. Specifically, this study aims to better understand the airflow dynamics and how they couple with the vehicle dynamics. The pneumatic model is coupled with a roll-plane model of the truck to evaluate the effect of the suspension pneumatic dynamics on the body roll, as well as the force transmission to the sprung mass. The results of the study show that maintaining a balanced airflow through the suspension improves the dynamic responsiveness of the suspension to steering, causing less body roll.
Dynamic Response Optimization of Complex Multibody Systems in a Penalty Formulation Using Adjoint Sensitivity
Zhu, Yitao; Dopico, Daniel; Sandu, Corina; Sandu, Adrian (ASME, 2015-05-01)
Imparting motion to a test object such as a motor vehicle in a controlled fashion with improved accuracy
(United States Patent and Trademark Office, 2017-05-09)
An apparatus imparts motion to a test object such as a motor vehicle in a controlled fashion. A base has mounted on it a linear electromagnetic motor having a first end and a second end, the first end being connected to the base. A pneumatic cylinder and piston combination have a first end and a second end, the first end connected to the base so that the pneumatic cylinder and piston combination is generally parallel with the linear electromagnetic motor. The second ends of the linear electromagnetic motor and pneumatic cylinder and piston combination being commonly linked to a mount for the test object. A control system for the linear electromagnetic motor and pneumatic cylinder and piston combination drives the pneumatic cylinder and piston combination to support a substantial static load of the test object and the linear electromagnetic motor to impart controlled motion to the test object.
A simulation-based comparative study on lateral characteristics of trucks with double and triple trailers
Chen, Yang; Peterson, Andrew W.; Zhang, Ce; Ahmadian, Mehdi (Inderscience Publishers, 2019-01-01)
This paper investigates the lateral stability and manoeuvrability in long combination vehicles (LCVs), namely semi-trucks with 28-ft doubles, 28- ft triples, and 33-ft doubles, using TruckSim. In particular, the likelihood of rollovers, rearward amplification, and off-tracking are analysed among those LCVs using the multi-domain dynamic models developed in TruckSim. The efforts to validate the truck dynamic model against test results are also included. The simulation results show that trucks with triple trailers exhibit a larger rearward amplification, higher likelihood of rollovers, and larger offtracking than trucks with double trailers. Additionally, the results indicate that increasing the trailer length from 28 to 33 feet does not increase the likelihood of rollovers or the rearward amplification. In fact, the longer trailers provide a slight amount of additional roll stability due to their longer wheelbase.
Simulation Evaluation on the Rollover Propensity of Multi-Trailer Trucks at Roundabouts
Chen, Yang; Zheng, Xiaohan; Peterson, Andrew; Ahmadian, Mehdi (SAE International, 2019-01-01)
The main intent of this study is to provide a simulation analysis of rollover dynamics of multi-trailer commercial vehicles in roundabouts. The results are compared with conventional tractor-semitrailer with a single 53-ft trailer for roundabouts that are of typical configuration to those in the U.S. cities. The multi-trailer commercial vehicles that are considered in this study are the A-double trucks commonly operated in the U.S. roads with the trailer length of 28 ft, 33 ft, and 40 ft. The multi-body dynamic models for analyzing the rollover characteristics of the trucks in roundabouts are established in TruckSim®. The models are intended to be used to assess the maximum rollover indexes of each trailer combination subjected to various circulating speeds for two types of roundabouts, 140-ft single-lane and 180-ft double-lane. The simulation results suggest that the 40-ft double has rollover speed thresholds 2-9 mph lower (more vulnerable to rolling over) as compared with the conventional 53-ft semi-trailer-truck. The lower roll stability for the 40-ft A-train configuration is attributed to its pintle-hitch coupling that allows for a certain amount of roll degree of freedom between the front and rear trailers. In addition, the worse tracking performance of the 40-ft double due to its longer wheelbase contributes to the heavier use of truck apron, greatly increasing the chance of rollover. The results also indicate that the 28-ft and 33-ft double-trailer trucks possess better maneuverability (less off-tracking) and can tolerate the rollover speed 1-3 mph higher than that of the 53-ft single-trailer truck. Furthermore, it is found that increasing the trailer from 28 ft to 33 ft results in the truck slightly less prone to rollover crashes, because of their longer wheelbase providing a slight amount of additional roll stability.
Failure mode and effects analysis of dual levelling valve airspring suspensions on truck dynamics
Chen, Yang; Hou, Yunbo; Peterson, Andrew W.; Ahmadian, Mehdi (Taylor & Francis, 2019-04-03)
Failure mode and effects analysis are performed for a dual levelling valve pneumatic suspension to determine the effect of suspension failure on tractor–semi-trailer dynamics, using a detailed model of suspension pneumatics coupled with a truck dynamic model. A key element of failure analysis in suspensions with one or two levelling valves is determining the effect on the vehicle body roll when one or more failures occur. The failure modes considered are mainly the suspension pneumatic components, including clogged levelling valve, bent control rod, disabled lever arm, and punctured or leaking connectors and pipes. The pneumatic suspension is modelled in AMESim, with critical parameters established through component testing. Upon validating the AMESim component model experimentally, the pneumatic suspension model is integrated into TruckSim for studying the consequences of suspension failure on truck dynamics. The simulation results indicate that the second levelling valve in a dual-valve arrangement brings a certain amount of failure redundancy to the system, in the sense that when one side fails, the other side can compensate for the failure. Equipping the trailer with dual levelling valves brings an additional stabilising effect to the vehicle in the event of tractor suspension failure.
Countering the Destabilizing Effects of Shifted Loads through Pneumatic Suspension Design
Chen, Yang; Ahmadian, Mehdi (SAE International, 2019-11-08)
This article proposes a novel approach to reduce the destabilizing impacts of the shifted loads of heavy trucks (due to improper loading or liquid slosh) by pneumatic suspension design. In this regard, the pneumatically balanced suspension with dual leveling valves is introduced, and its potential for the improvement of the body imbalance due to the shifted load is determined. The analysis is based on a multi-domain model that couples the suspension fluid dynamics, shifted-load impacts, and tractor-semitrailer dynamics. Truck dynamics is simulated using TruckSim, which is integrated with the pneumatic suspension model developed in AMESim. This yields a reasonable prediction of the effect of the suspension airflow dynamics on vehicle dynamics. Moreover, the ability of the pneumatic suspension to counteract the effects of two general shifted loads - static (rigid cargo) and dynamic (liquid) - is studied. The simulation results indicate that the dual-leveling-valve suspension results in a reduction in roll angle and roll rate of the vehicle body for both static and dynamic load-shifting cases, as compared to the conventional single-leveling-valve suspension. Suppression of the liquid sloshing behavior is obtained by the truck with the dual-leveling-valve suspension. Furthermore, the co-simulation platform established in the study is useful for efficient and accurate analyses of the coupled shifted load-pneumatic suspension-vehicle system dynamics.
Achieving anti-roll bar effect through air management in commercial vehicle pneumatic suspensions
Chen, Yang; Peterson, Andrew W.; Ahmadian, Mehdi (Taylor & Francis, 2019-12-02)
This paper introduces the concept of managing air in commercial vehicle suspensions for reducing body roll. A conventional pneumatic suspension is re-designed to include higher-flow air hoses and dual levelling valves for improving the dynamic response of the suspension to the body roll, which commonly happens at relatively low frequencies. The improved air management allows air to get from the air tank to the airsprings quicker, and also changes the side-to-side suspension air pressure such that the suspension forces can more readily level the vehicle body, much in the same manner as an anti-roll bar (ARB). The results of a multi-domain simulation study in AMESim and TruckSim indicate that the proposed suspension configuration is capable of providing balanced airflow to the truck’s drive-axle suspensions, resulting in balanced suspension forces in response to single lane change and steady-state cornering steering maneuvers. The simulation results further indicate that a truck equipped with the reconfigured suspension experiences a uniform dynamic load sharing, smoother body motion (less roll angle), and improved handling and stability during steering maneuvers commonly occurring in commercial trucks during their intended use.
Comparative Analysis of Emergency Evasive Steering for Long Combination Vehicles
Chen, Yang; Zhang, Zichen; Ahmadian, Mehdi (SAE International, 2020-10-10)
This study provides a simulation-based comparative analysis of the distance and time needed for long combination vehicles (LCVs) - namely, A-doubles with 28-, 33-, and 48-ft trailers - to safely exercise an emergency, evasive steering maneuver such as required for obstacle avoidance. The results are also compared with conventional tractor-semitrailers with a single 53-ft trailer. A multi-body dynamic model for each vehicle combination is developed in TruckSim® with an attempt to assess the last point to steer (LPTS) and evasive time (ET) at various highway speeds under both dry and wet road conditions. The results indicate that the minimum avoidance distance and time required for the 28-ft doubles vary from 206 ft (60 mph) to 312 ft (80 mph) and 2.3 s to 2.6 s, respectively. The required LPTS represents a 6% to 31% increase when compared with 53-ft semitrucks. When driving below 76 mph on a dry road and below 75 mph on a wet road, the 28-ft doubles exhibit LPTS and ET that are larger than 33-ft doubles. In addition, the 33-ft doubles exhibit larger LPTS and ET than 48-ft doubles for the highway speeds considered. This is mainly attributed to the longer trailer wheelbase that causes smaller rear trailer amplifications. At speeds higher than 76 mph on dry roads and 75 mph on wet roads, however, an opposite trend is observed. As the trailer length increases, the distance and time needed to safely avoid an obstacle also increase. A comparison between dry and wet road conditions is also conducted, with the results indicating that more time and distance would be needed for obstacle avoidance on wet roads.
Isolation Properties of Low-Profile Magnetorheological Fluid Mounts
Ahmadian, Mehdi; Southern, Brian M. (MDPI, 2021-04-19)
This study evaluates the stiffness and damping characteristics of low-profile magnetorheological (MR) fluid mounts (MRFM) to provide a better understanding of the vibration improvements offered by such mounts, as compared with conventional elastomeric mounts. It also aims at assessing how much of the mount’s performance is due to the MR fluid and how much is due to the elastomer and steel insert that is used in MRFM. The study includes the design, analysis, fabrication, and testing of a unique class of MRFM that is suitable for the isolation of sensitive machinery and sensors. The MR fluid is compressed (squeezed) in response to dynamic force applied to the mount. The test results are compared with conventional elastomeric (rubber) mounts of the same configuration as MRFM, to highlight the changes in stiffness and damping characteristics for frequencies ranging from 1 to 35 Hz. With no current supplied, the MRFM has a slightly higher stiffness and nearly the same damping as a conventional rubber mount. The slight increase in MRFM stiffness is attributed to the MR fluid’s compressive stiffness, which is higher than the rubber. When current is supplied to the MRFM, the stiffness and damping increase significantly at lower frequencies and taper off to nearly the same level as the rubber mount at higher frequencies. Both the stiffness and damping are directly proportional to the supplied current. At the maximum current of 2 A, the MRFM has 200% higher stiffness and 700% higher damping than the rubber mount. The significantly higher damping and stiffness and the tapering off to nearly the same level as the rubber mount is quite interesting and intriguing. It indicates that MRFM delivers high damping and stiffness when needed, while significantly tapering them off when high damping and stiffness are not desirable.
Detailed Modeling of Pneumatic Braking in Long Combination Vehicles
Zhang, Zichen; Sun, Nan; Chen, Yang; Ahmadian, Mehdi (SAE International, 2021-08-23)
A detailed model for pneumatic S-cam drum brake systems is developed and integrated into a multibody dynamic model for a 33-ft A-double long combination vehicle (LCV). The model, developed in TruckSim®, is used to study the dynamics of LCVs during straight-line braking at various speeds. It includes the response delay in braking that occurs from the time of application to when the brakes are applied at the drum for all axles. Additionally, the model incorporates an accurate characterization of brake torque versus chamber pressure at different speeds, along with the anti-lock brake system (ABS) dynamics, to yield an accurate prediction of the vehicle's deceleration during braking. The modeling results are compared with test results at speeds ranging from 20 mph to 65 mph on dry pavement. A close match between the model's prediction and test results is observed. The model is then used to perform a parametric study that evaluates braking distance and time for different pavement coefficients of friction (μp) at various speeds. The results indicate a distinct nonlinear relationship between μp and braking dynamics. At various μp, stopping time increases linearly with speed, as perhaps expected. Stopping distance, however, increases nonlinearly for a larger μp and linearly for a smaller μp versus speed. At a given speed, stopping time increases nonlinearly with a reduced μp, whereas stopping distance increases relatively linearly with a reduced μp.
Quantifying the effect of roadway, driver, vehicle, and location characteristics on the frequency of longitudinal and lateral accelerations
Ali, Gibran; McLaughlin, Shane B.; Ahmadian, Mehdi (Pergamon-Elsevier, 2021-10-01)
The purpose of this study is to understand and quantify the simultaneous effects of roadway speed category, driver age, driver gender, vehicle class, and location on the rates of longitudinal and lateral acceleration epochs. The rate of usual as well as harsh acceleration epochs are used to extract insights on driving risk and driver comfort preferences. However, an analysis of acceleration rates at multiple thresholds incorporating various effects while using a large-scale and diverse dataset is missing. This analysis will fill this research gap. Data from the 2nd Strategic Highway Research Program Naturalistic Driving Study (SHRP2 NDS) was used for this analysis. The rate of occurrence of acceleration epochs was modeled using negative binomial distribution based generalized linear mixed effect models. Roadway speed category, driver age, driver gender, vehicle class, and location were used as the fixed effects and the driver identifier was used as the random effect. Incidence rate ratios were then calculated to compare subcategories of each fixed effect. Roadway speed category has the strongest effect on longitudinal and lateral accelerations of all magnitudes. Acceleration epoch rates consistently decrease as the roadway speed category increases. The difference in the rates depends on the threshold and is up to three orders of magnitude. Driver age is another significant factor with clear trends for longitudinal and lateral acceleration epochs. Younger and older drivers experience higher rates of longitudinal accelerations and decelerations. However, the rate of lateral accelerations consistently decreases with age. Vehicle class also has a significant effect on the rate of harsh accelerations with minivans consistently experiencing lower rates.
A statistical evaluation of multiple regression models for contact dynamics in rail vehicles using roller rig data
Hosseini, Sayed Mohammad; Radmehr, Ahmad; Ahangarnejad, Arash Hosseinian; Gramacy, Robert B.; Ahmadian, Mehdi (Taylor & Francis, 2022-01-06)
A statistical analysis of a large amount of data from experiments conducted on the Virginia Tech-Federal Railroad Administration (VT-FRA) roller rig under various field-emulated conditions is performed to develop multiple regression models for longitudinal and lateral tractions. The experiment-based models are intended to be an alternative to the classical wheel-rail contact models that have been available for decades. The VT-FRA roller rig data is used to develop parametric regression models that efficiently capture the relationship between traction and the combined effects of the influential variables. Single regression models for representing the individual effect of wheel load, creepage, and angle of attack on longitudinal and lateral traction were investigated by the authors in an earlier study. This study extends single regression models to multiple regression models and assesses the interaction among the variables using model selection approaches. The multiple-regression models are then compared with CONTACT, a well-known modelling tool for contact dynamics, in terms of prediction accuracy. The predictions made by both CONTACT and multiple regression models for longitudinal and lateral tractions are in close agreement with the measured data on the VT-FRA roller rig. The multiple regression model, however, offers an algebraic expression that can be solved far more efficiently than a simulation run in CONTACT for a new dynamic condition. The results of the study further indicate that the established multiple regression models are an effective means for studying the effect of multiple parameters such as wheel load, creepage, and angle of attack on longitudinal and lateral tractions. Such data-driven parametric models provide an essential analysis and engineering tool in contact dynamics, just as they have in many other areas of science and engineering.
Mechanical Design & Fabrication of Redressing System for the VT-FRA Roller Rig
Jones, Dwight W.; Ahmadian, Mehdi; Molzon, Michael (Virginia Tech, 2022-01-31)
At the Center for Vehicle Systems and Safety at Virginia Tech, the Virginia Tech – Federal Railroad Administration Roller Rig is a state of the art facility used in evaluating the wheel-rail mechanics and dynamics of railway vehicle and track. Consisting of an upper wheel, a lower roller, and multiple actuators/servos, the Roller Rig is fitted with sensors that measure different parameters from force, rotation speed, and more. However, while the Roller Rig is a fitting device for a multitude of scientific and engineering studies related to railway vehicles, wheel-rail interaction while the Roller Rig is in operation, creates a rough wear band that is visible both to the naked eye, and on the micron level with the use of laser scanners. With the presence of this wear band, before the start of each experiment, a process known as redressing must be performed to smooth the surface of the wheel. This process is necessary to promote data precision and consistency throughout experiments. Previously, this process was done entirely manually, with the individual wrapping various grades of sandpaper around a common PVC pipe and applying pressure while the Roller Rig’s wheel spins. This is done with a total of 5 grades of sandpaper, varying from 40 grit up to 220 grit. As one can imagine, this process is incredibly labor intensive and presents many concerns related to safety, worker productivity, and overall precision and consistency of the redressing process. This paper will look at the development of a device to perform this redressing process in a semi-automatic, hands-off manner. Through initial brainstorming and concept generation to fabrication methods and manufacturing, this paper looks at the different the Roller Rig Redresser project throughout the entire engineering design process.
Video Image System Implementation on the Track Crawler Robot
Jones, Dwight W.; Mehdi, Ahmadian; Molzon, Michael; Larson, Ian (Virginia Tech, 2022-05-04)
The Track Crawler robot at the Center for Vehicle Systems and Safety, in Blacksburg, Virginia, is a state of the art project that is designed to examine the underbelly of trains while in a dormant state. The idea and motivation for this project comes from scenario that a train would arrive at a station, after completing a journey, and the Track Crawler robot would navigate under the train to examine the systems within to allow engineers to determine if parts of the train require extra maintenance before its next journey. Consequentially, the majority of the Track Crawler project is dependent on the proper function of the robot’s video imaging system. This system allows engineers to have a clear view of the underbelly of the theoretical train, in a space thatis otherwise not accessible to view by the naked human eye. On the current model of the Track Crawler, the robot is fitted with up to 3 GoPro Hero 8 Black Cameras, aligned in a linear fashion, to work as the robot’s video imaging system. One of the major problems with this system, however, is the vibrations the system is put under while the robot is in motion, and effect it has on the quality of videos. Therefore, the scope of this report will be to give the reader an idea of how the problem was identified as well as outlining possible solutions for a new visual imaging system that includes a new standard video camera, an infrared camera, and an adjustable light sensor. All of these proposed additional systems will work to remedy the original problem of maintaining high video quality at high frequency vibrations, and this report will serve as a foundation for implementing a more detailed design in the future.
When is it too Late to Brake?
Chen, Yang; Zhang, Zichen; Neighborgall, Campbell; Ahmadian, Mehdi (2022-11)
This paper provides a simulation analysis of the braking action that would prevent untripped rollovers of long combination vehicles (LCV) in turns when the entry speed into a turn exceeds the vehicle’s threshold. A co-simulation model is used to integrate the details of truck pneumatic brakes into a TruckSim® model. The brake system model is developed in Simulink. Both the TruckSim® and Simulink models are validated using data from field tests. Using the validated models, various braking initiation times (relative to the start of steering) are performed for a 150-ft J-turn. The J-turn simulates an exit ramp or curved roadway. The simulation results reveal that at higher speeds, there is very little time for the driver to initiate braking before it is too late to avoid a rollover, referred to as the Critical Brake Initiation Time (CBIT). For instance, at an entry speed of 40 mph (64 km/hr), the driver of a fully-loaded truck has approximately 1.0s before recognizing that the speed is too excessive for the turn. Applying the brakes beyond this time would not prevent a rollover. The challenge often stems from the fact that for long combination vehicles, the driver can not accurately sense the trailer’s roll dynamics, which can greatly hinder the driver’s timely response to reducing speed to avoid rollovers. A key question is “when it is too late to brake?” To provide answers, various loading conditions and entry speeds are simulated. The results indicate that heavier loads that result in higher trailer CG require both lower entry speeds and sooner braking to avoid rollovers, somewhat as expected. The CBIT is highly influenced by the entry speed into a turn. For instance, for a fully-loaded LCV, increasing the speed by 20% from 40 mph (64 km/hr) to 50 mph (80 km/hr), reduces CBIT by 90%, from 1.0s to 0.1s. The effect of load on CBIT is less dramatic than speed. At 40 mph (64 km/hr), increasing the cargo load by 47%, from 15000 lb. (6800 kg) to 22000 lb. (10000 kg), decreases the CBIT by 20%, from 1.2s to 1.0s.

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