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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Browsing Center for Vehicle Systems and Safety (CVeSS) by Author "Chen, Yang"

Now showing 1 - 10 of 10
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
  • 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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    When is it too late to brake?
    Chen, Yang; Zhang, Zichen; Neighborgall, Campbell; Ahmadian, Mehdi (Taylor & Francis, 2022-11-22)
    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 (developed in Simulink®) in a TruckSim® model. The models are validated with  field-test data. Using the validated models, various braking initiation times (relative to the start of steering) are performed for a 150-ft J-turn. 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 Critical Brake Initiation Time (CBIT). For instance, at an entry speed of 40 mph (64 km/hr), applying the brakes for a fully-loaded truck beyond 1.0s would not prevent a rollover. The results also indicate that increasing the speed by 25% 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 cargo load on CBIT is less dramatic than speed. At 40 mph (64 km/hr), increasing the cargo load by 47%, from 15,000 lb. (6800 kg) to 22,000lb. (10,000 kg), decreases the CBIT by 17%, from 1.2s to 1.0s.