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Journal Article

Vehicle Stability Control through Optimized Coordination of Active Rear Steering and Differential Driving/Braking

2018-07-05
Abstract In this article, a hierarchical coordinated control algorithm for integrating active rear steering and driving/braking force distribution (ARS+D/BFD) was presented. The upper-level control was synthesized to generate the required rear steering angle and external yaw moment by using a sliding-mode controller. In the lower-level controller, a control allocation algorithm considering driving/braking actuators and tire forces constraints was designed to assign the desired yaw moment to the four wheels. To this end, an optimization problem including several equality and inequality constraints were defined and solved analytically. Finally, computer simulation results suggest that the proposed hierarchical control scheme was able to help to achieve substantial enhancements in handling performance and stability.
Journal Article

Vehicle Aerodynamic Optimization: On a Combination of Adjoint Method and Efficient Global Optimization Algorithm

2019-04-26
Abstract This article presents a workflow for aerodynamic optimization of vehicles that for the first time combines the adjoint method and the efficient global optimization (EGO) algorithm in order to take advantage of both the gradient-based and gradient-free methods for aerodynamic optimization problems. In the workflow, the adjoint method is first applied to locate the sensitive surface regions of the baseline vehicle with respect to the objective functions and define a proper design space with reasonable design variables. Then the EGO algorithm is applied to search for the optimal site in the design space based on the expected improvement (EI) function. Such workflow has been applied to minimize the aerodynamic drag for a mass-produced electric vehicle. With the help of STAR-CCM+ and its adjoint solver, sensitive surface regions with respect to the aerodynamic drag are first located on the vehicle.
Journal Article

U.S. Light-Duty Vehicle Air Conditioning Fuel Use and Impact of Solar/Thermal Control Technologies

2018-12-11
Abstract To reduce fuel consumption and carbon dioxide (CO2) emissions from mobile air conditioning (A/C) systems, “U.S. Light-Duty Vehicle Greenhouse Gas Emissions and Corporate Average Fuel Economy Standards” identified solar/thermal technologies such as solar control glazings, solar reflective paint, and active and passive cabin ventilation in an off-cycle credit menu. National Renewable Energy Laboratory (NREL) researchers developed a sophisticated analysis process to calculate U.S. light-duty A/C fuel use that was used to assess the impact of these technologies, leveraging thermal and vehicle simulation analysis tools developed under previous U.S. Department of Energy projects. Representative U.S. light-duty driving behaviors and weighting factors including time-of-day of travel, trip duration, and time between trips were characterized and integrated into the analysis.
Journal Article

Transient Operation and Over-Dilution Mitigation for Low-Pressure EGR Systems in Spark-Ignition Engines

2018-09-17
Abstract Low-Pressure cooled Exhaust Gas Recirculation (LP-cEGR) is proven to be an effective technology for fuel efficiency improvement in turbocharged spark-ignition (SI) engines. Aiming to fully exploit the EGR benefits, new challenges are introduced that require more complex and robust control systems and strategies. One of the most important restrictions of LP-cEGR is the transient response, since long air-EGR flow paths introduce significant transport delays between the EGR valve and the cylinders. High dilution generally increases efficiency, but can lead to cycle-by-cycle combustion variation. Especially in SI engines, higher-than-requested EGR dilution may lead to combustion instabilities and misfires. Considering the long EGR evacuation period, one of the most challenging transient events is throttle tip-out, where the engine operation shifts from a high-load point with high dilution tolerance to a low-load point where EGR tolerance is significantly reduced.
Journal Article

Systematic CFD Parameter Approach to Improve Torque Converter Simulation

2019-04-08
Abstract A systematic parametrization approach was employed to simulate a torque converter operating over a wide range of speed ratios. Results of the simulation yielded torque converter impeller and turbine torques prediction errors below 11% when compared to manufacturer data. Further improvements in the computational fluids dynamic (CFD) model reduced such errors down to 3% for the impeller and 6% for the turbine torque predictions. Convergence was reached well under 300 iterations for the most optimal variable setting, but each speed ratio was let to run for 300 iterations. Solution time for the 300 iterations was 40 minutes per speed ratio. The systematic parametrization provides a very competitive procedure for torque converter simulation with reduced computational error and fast solution time.
Journal Article

Steady Aeroelastic Response Prediction and Validation for Automobile Hoods

2018-07-10
Abstract The pursuit of improved fuel economy through weight reduction, reduced manufacturing costs, and improved crash safety can result in increased compliance in automobile structures. However, with compliance comes an increased susceptibility to aerodynamic and vibratory loads. The hood in particular withstands considerable aerodynamic force at highway speeds, creating the potential for significant aeroelastic response that may adversely impact customer satisfaction and perception of vehicle quality. This work seeks an improved understanding in computational and experimental study of fluid-structure interactions between automobile hoods and the surrounding internal and external flow. Computational analysis was carried out using coupled CFD-FEM solvers with detailed models of the automobile topology and structural components. The experimental work consisted of wind tunnel tests using a full-scale production vehicle.
Journal Article

Speed Planning and Prompting System for Commercial Vehicle Based on Real-Time Calculation of Resistance

2019-06-25
Abstract When commercial vehicles drive in a mountainous area, the complex road condition and long slopes cause frequent acceleration and braking, which will use 25% more fuel. And the brake temperature rises rapidly due to continuous braking on the long-distance downslopes, which will make the brake drum fail with the brake temperature exceeding 308°C [1]. Meanwhile, the kinetic energy is wasted during the driving progress on the slopes when the vehicle rolls up and down. Our laboratory built a model that could calculate the distance from the top of the slope, where the driver could release the accelerator pedal. Thus, on the slope, the vehicle uses less fuel when it rolls up and less brakes when down. What we do in this article is use this model in a real vehicle and measure how well it works.
Journal Article

Passive Flow Control on a Ground-Effect Diffuser Using an Inverted Wing

2018-08-13
Abstract In this experimental and computational study a novel application of aerodynamic principles in altering the pressure recovery behavior of an automotive-type ground-effect diffuser was investigated as a means of enhancing downforce. The proposed way of augmenting diffuser downforce production is to induce in its pressure recovery action a second pressure drop and an accompanying pressure rise region close to the diffuser exit. To investigate this concept with a diffuser-equipped bluff body, an inverted wing was situated within the diffuser flow channel, close to the diffuser exit. The wing’s suction surface acts as a passive flow control device by increasing streamwise flow velocity and reducing static pressure near the diffuser exit. Therefore, a second-stage pressure recovery develops along the diffuser’s overall pressure recovery curve as the flow travels from the diffuser’s low pressure, high velocity inlet to its high pressure, low velocity exit.
Journal Article

Parametric Study of Asymmetric Side Tapering in Constant Cross Wind Conditions

2018-06-28
Abstract Sports Utility Vehicles (SUVs) often have blunt rear end geometries for design and practicality, which is not typically aerodynamic. Drag can be reduced with a number of passive and active methods, which are generally prioritised at zero yaw, which is not entirely representative of the “on road” environment. As such, to combine a visually square geometry (at rest) with optimal drag reductions at non-zero yaw, an adaptive system that applies vertical side edge tapers independently is tested statically. A parametric study has been undertaken in Loughborough University’s Large Wind Tunnel with the ¼ scale Windsor Model. The aerodynamic effect of implementing asymmetric side tapering has been assessed for a range of yaw angles (0°, ±2.5°, ±5° and ±10°) on the force and moment coefficients.
Journal Article

Obstacle Avoidance for Self-Driving Vehicle with Reinforcement Learning

2017-09-23
Abstract Obstacle avoidance is an important function in self-driving vehicle control. When the vehicle move from any arbitrary start positions to any target positions in environment, a proper path must avoid both static obstacles and moving obstacles of arbitrary shape. There are many possible scenarios, manually tackling all possible cases will likely yield a too simplistic policy. In this paper reinforcement learning is applied to the problem to form effective strategies. There are two major challenges that make self-driving vehicle different from other robotic tasks. Firstly, in order to control the vehicle precisely, the action space must be continuous which can’t be dealt with by traditional Q-learning. Secondly, self-driving vehicle must satisfy various constraints including vehicle dynamics constraints and traffic rules constraints. Three contributions are made in this paper.
Journal Article

Numerical and Experimental Investigation of the Optimization of Vehicle Speed and Inter-Vehicle Distance in an Automated Highway Car Platoon to Minimize Fuel Consumption

2018-06-22
Abstract The development of the technology of automated highways promises the opportunity for the vehicles to travel safely at a closer distance concerning each other. As such, vehicles moving in the wake of others experience a reduction in fuel consumption. This article investigates the effect of longitudinal distance between two passenger cars on drag coefficients numerically and experimentally. For the numerical analysis, the fluid flow at car speeds of 70, 90 and 110 km/h were examined. The Artificial Intelligence coding was applied to train an Artificial Neural Network to extend the calculated data. The optimum values for the inter-vehicle distance and the vehicle speed to assure the least drag coefficient are obtained. To support the numerical results an instrument designed and built particularly to accurately measure the fuel consumption was installed on a midsize sedan car and some field tests were carried out.
Journal Article

Numerical Investigation of the Characteristics of Spray/Wall Interaction with Hybrid Breakup Model by Considering Nozzle Exit Turbulence

2018-12-04
Abstract The spray/wall interaction plays a significant role on the mixture formation, combustion, and exhaust emissions. In the present study, the numerical code General Transport Equation Analysis (GTEA) is used to investigate the effect of fuel primary spray on the spray/wall interaction process. Taylor Analogy Breakup (TAB) model, Kelvin-Helmholtz-Rayleigh-Taylor (KH-RT) model, and Hybrid breakup (Hybrid) model are used to simulate the fuel spray process. By comparing the radius and height of the impinged spray, the performance of these breakup models is evaluated. Then, Bai and Gosman (BG) and Zhang and Jia (ZJ) spray/wall interaction models are implemented into GTEA code to describe the complicated spray/wall interaction process, and these interaction models are validated by the radius and height of the impinged spray and the size and velocity of the secondary droplets.
Journal Article

Methodology for Developing a Diesel Exhaust After Treatment Simulation Tool

2017-09-16
Abstract A methodology for the development of catalyst models is presented. Also, a methodology of the implementation of such models into a modular simulation tool, which simulates the units in succession, is presented. A case study is presented illustrating how suitable models can be found and used for simulations. Such simulations illustrate the behavior of the individual units and the overall system. It is shown how, by simulating the units in succession, the entire after treatment system can be tested and optimized, because the integration makes it possible to observe the effect of the modules on one another.
Journal Article

Limitations of Two-Stage Turbocharging at High Flight Altitudes

2018-09-17
Abstract High-altitude long-endurance (HALE) unmanned aerial vehicles (UAVs) are used for high flight altitudes, which enable low drag and fast flight with minimal fuel consumption. Two-stage turbocharging is necessary to sustain sea-level power at high flight altitudes. In this study, the limitations of two-stage turbocharging at high flight altitudes typical for HALE UAVs are analyzed for the first time. The obtained results show that the minimum available engine power increases as the altitude rises. This will limit the ability of the aircraft to descend rapidly. Furthermore, at high altitudes, if a lower operating point is required for a fast descent, further recovery to full power for climbing or cruising could be unavailable. In the latter cases, a lower altitude must be reached before full power would be available again. A basic algorithm for the assessment and analysis of the limitations of UAV engines with two-stage turbochargers operating at high altitudes is suggested.
Journal Article

Landing Response Analysis on High-Performance Aircraft* Using Estimated Touchdown States

2019-04-08
Abstract A novel use of state estimation methods as initial input for a landing response analysis is proposed in this work. Six degrees of freedom (DOF) non-linear landing response model is conceived by considering longitudinal dynamics of aircraft as a rigid body with heave-and-pitch motions coupled onto a bicycle landing gear † arrangement. The DOF for each landing gear consist of vertical and longitudinal motions of un-sprung mass, considering strut bending flexibility. The measurement data for state estimation is obtained for three landing cases using non-linear flight mechanics model interfaced with pilot-in-loop simulation. State estimation methods such as Upper Diagonal Adaptive Extended Kalman Filter (UD-AEKF) with fuzzy-based adaptive tuning and Un-scented Kalman Filter (UKF) were adapted for landing maneuver problem. On the basis of estimation error metrics, aircraft state from UKF is considered during onset of touchdown.
Journal Article

Investigation on Underhood Thermal Analysis of Truck Platooning

2018-03-22
Abstract This paper presents a combined aero-thermal computational fluid dynamic (CFD) evaluation of platooning medium duty commercial vehicles in two highway configurations. Thermal analysis comparison is made between an approach that includes vehicle drag reduction on engine heat rejection and one that does not by assuming a constant heat rejection based on open road conditions. The paper concludes that accounting for aerodynamic drag reduction on engine heat load provides a more real world evaluation than assuming a constant heat load based on open road conditions. A 3D CFD underhood thermal simulations are performed in two different vehicle platooning configurations; (i) single-lane and (ii) two-lane traffic conditions. The vehicle platooning consists of two identical vehicles, i.e. leading and trailing vehicle. In this work, heat exchangers are modeled by two different heat rejection rate models.
Journal Article

Investigation of Passive Porosity as a Means for Bluff-Body Drag Reduction

2018-03-16
Abstract An investigation into the capability of passive porosity to reduce the drag of a bluff-body is presented. This initial work involves integrating varying degrees of porosity into the side and back faces of a small-scale model to determine optimum conditions for maximum drag reduction. Both force and pressure measurements at differing degrees of model yaw are presented, with the conditions for optimum performance, identified. At a length-based Reynolds number of 2.3 × 106, results showed a maximum drag reduction of 12% at zero yaw when the ratio of the open area on the back face relative to the side faces was between two and four. For all non-zero yaw angles tested, this ratio reduced to approximately two, with the drag benefit reducing to 6% at 10.5 degrees. From a supplementary theoretical analysis, calculated optimum bleed rate into the base for maximum drag reduction, also showed reasonable agreement to other results reported previously.
Journal Article

Integrated Positioning Method for Intelligent Vehicle Based on GPS and UWB

2017-09-23
Abstract Knowledge of intelligent vehicle absolute position is a vital premise for the implementation of decision programming, kinematic and dynamics control. In order to achieve high accuracy positioning and reduce running cost as much as possible under all operating conditions, this paper proposed an integrated positioning method based on GPS and Ultra Wide Band(UWB) for intelligent vehicle’s navigation and position system. In this method, GPS and UWB are alternately active according to the confidence level of GPS signal. When the vehicle is traveling in a wide-open area and GPS signal is well received, the positioning results of Dead Reckoning system are corrected by the low frequency positioning output from GPS. During the correcting process, in order to realize the better fusion of measurement data, a simplified federal Kalman filter was designed by using indirect method.
Journal Article

Influence of Intelligent Active Suspension System Controller Design Techniques on Vehicle Braking Characteristics

2018-12-04
Abstract This article presents a comprehensive investigation for the interaction between vehicle ride vibration control and braking control using two degrees of freedom (2DOF) quarter vehicle model. A typical limited bandwidth active suspension system with nonlinear spring and damping characteristics of practical hydraulic and pneumatic components is controlled to regulate both suspension and tire forces and therefore provide the optimum ride comfort and braking performance of an anti-lock brake system (ABS). In order to design a suitable controller for this nonlinear integrated system, various control techniques are followed including state feedback tuned using Linear Quadratic Regulator (LQR), state feedback tuned using Genetic Algorithm (GA), Proportional Integrated (PI) tuned genetically, and Fuzzy Logic Control (FLC). The ABS control system is designed to limit skid ratio below threshold of 15%.
Journal Article

Improving Vehicle Rollover Resistance Using Fuzzy PID Controller of Active Anti-Roll Bar System

2018-12-20
Abstract The active anti-roll bar (AARB) system in vehicles has recently become one of the research hotspots in the field of vehicle technology to improve the vehicle’s active safety. In most off-road vehicles, high ground clearance is required while keeping all wheels in contact with the ground in order to improve traction and maintain load distribution among the wheels. A problem however arises in some types of the off-road vehicles when the vehicle is operated at high speeds on smooth roads. In such condition, the combination of the vehicle’s center of gravity position, large suspension stroke, and soft spring construction creates a stability problem, which could make the vehicle liable to rollover. This article analyzes a comparison of stability performance between passive and active anti-roll bar systems to improve rolling resistance. For active systems, two control strategies will be investigated. The conventional PID controller is firstly investigated and taken as a reference.
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