Requirements for Vehicle Dynamics Simulation Models

<div class="htmlview paragraph">In racetrack conditions, brake systems are subjected to extreme energy loads and energy load distributions. This can lead to very high friction surface temperatures, especially on the brake corner that operates, for a given track, with the most available traction and the highest energy loading. Individual brake corners can be stressed to the point of extreme fade and lining wear, and the resultant degradation in brake corner performance can affect the performance of the entire brake system, causing significant changes in pedal feel, brake balance, and brake lining life. It is therefore important in high performance brake system design to ensure favorable operating conditions for the selected brake corner components under the full range of conditions that the intended vehicle application will place them under.</div> <div class="htmlview paragraph">To address this task in an early design stage, it is helpful to use brake system modeling tools to analyze system performance. Traditional modeling approaches have relied upon simple mathematical representation of measured brake corner output and fluid displacement (data which often result from inertia dyno testing) to predict system level performance. Many brake system analysis tools also include only a quasi-static two-dimensional vehicle dynamics model and do not fully capture cornering influences on braking energy load distribution. This paper will present a method of measuring brake corner output and compliance behavior during high energy usage conditions on a brake dynamometer and representing this behavior with neural network models. The resulting models are integrated with a fully 3-dimensional vehicle dynamics and 1-dimensional brake thermal model to result in significantly more accurate brake system performance predictions that include the vehicle dynamics influences on brake corner energy loading, brake corner responses such as in-stop fade and recovery, and in-stop lining wear and its influence on compliance.</div> <div class="htmlview paragraph">The resultant integrated neural-network brake corner and vehicle dynamics model is demonstrated in both straight-line braking events and simple race track simulations.</div>

<div class="htmlview paragraph">Motorized transport has become an essential part of our world economic system with an ever-increasing number of vehicles on the road. However, considering the depletion of energy resources and the aggravation of greenhouse gas issues, it is critical to improve vehicle fuel consumption. These demands are moving us toward advanced engine and powertrain technologies. However, understanding our progress also requires improvements in the way we measure and certify vehicle emissions and fuel economy performance.</div> <div class="htmlview paragraph">This paper describes the use of an on-board fuel consumption and emissions measurement system to develop on-road fuel consumption functions that can be used to quantify the fuel economy impact of vehicle, road and traffic control changes. The system uses an ECM OBD-II scanner, a Mass Air Flow meter and an emissions analyzer to monitor fuel consumption and exhaust CO<sub>2</sub> emission rates (in g/s) as well as vehicle speed and other parameters. All measurements are coordinated and recorded using a laptop computer. Vehicle tractive power is calculated from speed measurements using vehicle dynamic models, allowing calculation of actual fuel efficiency. In the results, the measured CO<sub>2</sub> emission values correlate well with those predicted by a carbon balance from measured fuel consumption, confirming the validity of a range of measurements.</div> <div class="htmlview paragraph">This paper reports on fuel consumption behaviors for five typical vehicles over seventy repeated tests in urban, highway and aggressive driving situations. Although it is well known that vehicle energy demand goes up with increasing steady speed, the results show the strong importance of fuel efficiency, vehicle accelerations and idle periods for actual on-road fuel consumption. Fuel efficiency is essentially zero at idle but rises to a high level for vehicle tractive power over 30% of the rated power. This trend indicates the potential for reduced fuel consumption through engine down-sizing and powertrain controls. For vehicles running in normal traffic situations, the fuel consumption tends to be best in the 60 km/h to 100 km/h <i>average vehicle speed</i> range due to the reduced severity of accelerations and lack of idling. Those results emphasize the potential for fuel savings through improvements of road structure and traffic control to reduce congestion. The test results are used to generate a fuel consumption model based on a vehicle dynamic model and speed trace. This model can be used to quantify the fuel consumption and greenhouse gas CO<sub>2</sub> emission effect for changes in vehicle characteristics and on-road operating conditions.</div>

<div class="section abstract"><div class="htmlview paragraph">Virtual simulation is a fundamental tool for the development of new vehicles, both for individual components and for complete subsystems and full vehicles. Many software tools exist in the automotive sector to assess full-vehicle behavior and performance, including multibody software and algorithms based on 14 (or more) degrees-of-freedom vehicle dynamics models. In order to reproduce the testing maneuvers and typical vehicle mission, a key part of such simulation tools is the virtual driver algorithm. It is essential to implement a control logic that reproduces the handling response of the driver, so that the closed-loop maneuvers can be evaluated. However, the response of typical virtual drivers is not always similar to the human driving characteristics. Virtual driver algorithms can perform very fast, precise, and smooth steering and pedal actions, while humans display a more variable, delayed and often not optimal actions.</div><div class="htmlview paragraph">The aim of this article is to describe the concept and implementation of a novel human-like path planning model. The algorithm is developed in MATLAB environment, creating a function that obtains a human-like path and vision logic by setting some key-parameters. They are: Distance Factor, Widening Factor, Cutting Factor, Inner Smoothing Factor and Outer Smoothing Factor.</div><div class="htmlview paragraph">The parameters - essential to alter the shape of the trajectory described in a track - have their values attributed by fitting experimental data gathered during test sessions in a driving simulator. The vehicle model used to implement the path planning system is based on the VI-Grade CarRealTime environment, in co-simulation with MATLAB/Simulink, and the results indicate that the novel algorithm has a closer correlation with the DiL tests than the original virtual driver. The stronger correlation is confirmed also in the comparison between different human drivers, showing that the proposed strategy is robust to driving styles.</div><div class="htmlview paragraph">Among the potential applications of this new “human-like virtual driver” approach is the ability to better predict human driver response during tuning and optimization of vehicles and control systems, apart from a further understanding of human driving behavior useful for tasks like ADAS and autonomous driving.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Driver model has been developed since 1950s and quite a lot of attention has been attracted on this aspect. Today there is a body of knowledge regarding driver mathematic model. Since driving behavior is highly complex, involving psychology and physiology factors, it is not easy to use a simple driver model to represent all characteristic features comprehensively, according to the utilization of driver model, some assumptions are necessarily proposed in order to tackle the specific problem easily.</div><div class="htmlview paragraph">Optimal Preview Acceleration Driver Model was put forward based on the Preview-Following Theory proposed by Prof. Guo in 1983. This driver model is quite simple and easy to understand, and accurate for great curvature path following. However, recent study has shown that more work is needed to improve the path following ability for sharp corner or urgent corner (higher frequency steering input). This paper will investigate and analyze the Optimal Preview Acceleration Driver Model in details, and propose an improvement based on this classical driver model to make it suitable for more specific conditions, especially for urgent cornering. Finally, the modified driver model will be verified to be more capable of realizing high frequency steering behavior than the previous driver model.</div></div>

<div class="htmlview paragraph">The concept of the intelligent Vehicle/Highway System (IVHS) is a direct descendent of earlier work on “roadway automation”. Recent advances in a variety of technologies have now made automatic control of the operation of road vehicles a much more realistic proposition than it was even in the recent past. This paper begins by identifying three stages in the likely evolution of these advanced vehicle control systems (AVCS), showing how AVCS is related to the other IVHS functions. The technological elements of AVCS, corresponding to needed research and technology development work, are then described. The current international state of the art in these technologies is reviewed, and the paper concludes with a discussion of an evolutionary progression that could be followed to lead from present-day driving to the long-term concept of an automated freeway network.</div>

<div class="htmlview paragraph">Electric Power-Assisted Steering (EPAS) is a new power steering technology that will define the future of vehicle steering. The assist of EPAS is the function of the steering wheel torque and vehicle velocity. The assist characteristic of EPAS is set by control software, which is one of the key issues of EPAS. The straight-line type assist characteristic has been used in some current EPAS products, but its influence on the steering maneuverability and road feel hasn't been explicitly studied in theory.</div> <div class="htmlview paragraph">In this paper, the straight-line type assist characteristic is analyzed theoretically. Then a whole vehicle dynamic model used to study the straight-line type assist characteristic is built with ADAMS/Car and validated with DCF (Driver Control Files) mode of ADAMS/Car. Based on the whole vehicle dynamic model, the straight-line type assist characteristic's influence on the steering maneuverability and road feel is investigated. Based on the driver's request for the ideal relationship between steering wheel torque and vehicle velocity, the vehicle speed proportional coefficient of the assist characteristic can be determined by making steering wheel torque at different vehicle lateral acceleration agree with the request of the driver at a certain velocity. The target of this paper is analyzing the influence of the straight-line type assist characteristic on the steering maneuverability and road feel, and studying how to apply simulation method to determine the straight-line type assist characteristic of EPAS, which will direct and benefit the adjustment of the assist characteristic during the road test.</div>

This study evaluates traction control systems (TCSs) composed of either a wheel slip controller or a throttle valve controller, or an integrated controller of both systems. The dynamic characteristics of a vehicle and a TCS are evaluated using a proposed full car model that can simulate the responses of both front-wheel-drive and four-wheel-drive vehicles. A driver model is also modified to control the vehicle during tests on a road with split Coefficients. The results show that the brake TCS provides more acceleration on uniform slippery and split roads, but the yaw rate and the lateral off set are larger than those obtained when an engine TCS is used. When the vehicle is cornering and accelerating with the brake or engine TCS, understeer or oversteer occur, depending on the driving conditions. An integrated TCS prevents most of these problems and improved the stability and controllability of the vehicle. Four-wheel-drive vehicles exhibit better traction control than two-wheel-drive vehicles, but their steerability is reduced.

<div class="section abstract"><div class="htmlview paragraph">Offtracking is the term used to describe the difference in path radii between the leading and trailing axle of a vehicle as it maneuvers around a turn. This phenomenon probably has been observed from the time multi-axle vehicles first were constructed. As vehicles, particularly articulated trucks, have become larger and longer, and the urban environment has become more compact and crowded, practical safety concerns relating to offtracking have increased. The geometric design of streets and highways, and of parking lots and trucking yards, will be affected by the maximum offtracking of vehicles using those facilities. In some accident investigations, offtracking is a primary consideration.</div><div class="htmlview paragraph">Much of present offtracking analysis is based upon a “zero-speed” assumption. In other words, the magnitude of offtracking is computed simply as a kinematic problem, with no dynamic effects considered. When the problem is analyzed kinetically, offtracking <i>outside</i> the path of the preceding wheels (a kind of “oversteer”) can be computed, depending on vehicle speed and configuration. Effects of roadway superelevation and other three-dimensional terrain features can be included in computer simulations.</div><div class="htmlview paragraph">This paper summarizes the history of offtracking analysis, presents a review of calculation methods in the literature, and details the speed-dependent nature of offtracking for two articulated heavy trucks, utilizing three-dimensional computer simulation.</div></div>

<div class="section abstract"><div class="htmlview paragraph">In this paper, a comparison of three different hybrid powertrains is analysed. The numerical model is used to simulate powertrain behaviour in rail application, on a pre-set drive cycle, composed of many acceleration and decelerations, in order to test the components features.</div><div class="htmlview paragraph">The numerical model is dynamic and it is implemented in Matlab-Simulink environmental.</div><div class="htmlview paragraph">A proton exchange membrane fuel cell (FC) is used; it is the most used in transport applications, thanks to its lower temperature compared to the other fuel cell types, which allows fast start up operation and rapid demand changes. A standard supercapacitor (SC), given by higher power density, is utilized as the energy storage system (ESS), Regarding the battery (B), two types are considered, because the battery is used both as prime mover and main component of the ESS; Li-ion batteries are chosen, owing to their good trade-off between specific power and energy.</div><div class="htmlview paragraph">Therefore, three configurations, FC-SC, FC-B and B-SC, are analysed.</div><div class="htmlview paragraph">The vehicle model takes into account other components. The regenerative brake system is used to recover energy during the deceleration phases, and the auxiliary system is modelled in order to consider the consumption due to lighting, air conditioning, etc. The DC/DC converter is used to connect energy sources and load; it is unidirectional for the FC and bidirectional for the other sources. This is because the ESS provides power for the drive cycle and it stores energy provided by the FC (when the power demand is low) and recovered by the regenerative brake (in deceleration operation).</div><div class="htmlview paragraph">In addition, a control system is implemented, able to manage the entire system and set the power output of each source at each instant of time. It works in order to achieve good performance for each energy source, in terms of high efficiency and long lifetime. This means low power variations for the FC and a pre-set interval for the ESS state of charge.</div><div class="htmlview paragraph">At the end, the results achieved by the simulations (such as efficiency, state of charge, and hydrogen consumption) are discussed and analysed for the different configurations.</div></div>

<div class="htmlview paragraph">The “Magic Formula” concept is an elegant, empirical method of fitting tire data for inclusion in vehicle dynamics models. Its behavior as a function of parameter values is explained in detail in this paper.</div> <div class="htmlview paragraph">This paper presents the BNPS model, a modification of the Magic Formula concept, which has been fully automated on a personal computer. This allows the ready reduction of data into practical Magic Formula type models without any investment of engineering time.</div> <div class="htmlview paragraph">BNPS fitting example results are presented.</div>

<div class="htmlview paragraph">This paper describes a tire model designed for the full range of operating conditions under both on- and off-road surface conditions. The operating conditions include longitudinal and lateral slip, camber angle and normal load. The model produces tire forces throughout the adhesion range up through peak coefficient of friction, and throughout the saturation region to limit slide coefficient of friction. Beyond the peak coefficient of friction region, the off-road portion of the model simulates plowing of deformable surfaces at large side slip angles which can result in side forces significantly above the normal load (e.g., equivalent coefficients of friction greatly exceeding unity).</div> <div class="htmlview paragraph">The model allows changing the saturation function depending the surface currently encountered by a given tire in the vehicle dynamics model. Saturation functions can vary from the sharp peak function associated with radial tires on paved surfaces, to the exponential like saturation associated with various off-road surfaces. Smooth transition functions are provided between the adhesion and saturation regions, and logic is provided to ensure that tire force always opposes slip velocity no matter what operating condition is encountered.</div> <div class="htmlview paragraph">This paper describes the model functional characteristics and response to a range of operating conditions. Data sources for the model are discussed. Cases are run with a vehicle dynamics model to illustrate model response to changing surface conditions.</div>

<div class="htmlview paragraph">Improved performance creates a need for a limited slip differential for widespread application. Existing types suffer from the disadvantage of high cost and they are generally not well suited to front wheel drive applications.</div> <div class="htmlview paragraph">The ‘Suretrac’ differential meets this enhanced requirement. In this new design torque is transmitted through the unit using a cam and follower principle. Any relative rotation of the cams on the output shafts is opposed by friction forces which generate a torque ratio between the output shafts. The design is novel in using helical faces to give large contact areas and avoid high Hertzian stresses.</div> <div class="htmlview paragraph">The performance of this type of differential differs from viscous types or traction control because the torque difference is established before any relative motion takes place. The tyre dynamics dictate the torques generated so that the differential always provides the optimum torque balance. This maintains tyre adhesion and enhances directional stability and safety.</div> <div class="htmlview paragraph">The complexity of the shapes involved precludes machining as an economic production process, so nett shape forming methods are used. This also has to apply to the prototype phase, and so simultaneous engineering has been implemented throughout the product development.</div> <div class="htmlview paragraph">The operation of the differential should normally not impinge on the driver's consciousness, so the performance can only be established by special tests carried out with full instrumentation. These tests include acceleration with the wheels on different surfaces, “split mu”, and acceleration on a curve to give unequal wheel loading. Test results are presented. Durability tests have also been completed.</div> <div class="htmlview paragraph">The differential is shown to give substantial advantages in operation, is capable of being installed in the same space as a conventional differential and has a minimum additional cost and so should gain widespread acceptance in all types of vehicle.</div>

<div class="section abstract"><div class="htmlview paragraph">A previous paper on this topic presented the use of design of experiments (DOE) to evaluate the sensitivity of vehicle dynamics simulation of the postimpact motion of a vehicle that included high initial rotational rates. That investigation involved only one software package and thus was confined to one simulation model for the purposes of developing and refining the analysis method rather than including a variety of simulation models for broader application. This paper expands the application of the method to investigate the comparative behavior and sensitivity of several other vehicle dynamic simulation models commonly used in the field of crash reconstruction. The software packages included in the studies presented in this paper are HVE (SIMON and EDSMAC4), PC-Crash and VCRware. This paper will present the results of the study, conducted using DOE, involving these models. The eleven factors selected for the study presented here were chosen based largely on the results of the prior study. The experimental design was expanded from 16 trials to 32 trials to provide additional insight into the interactions between the factors. Three response variables were used: the <i>x</i>-coordinate, <i>y</i>-coordinate and total rotational displacement of the vehicle at rest.</div><div class="htmlview paragraph">The results of the analysis show the sensitivity of all four programs to the eleven factors as well as the interactions between the factors. The results show that, consistent with prior results, and the expectation of the authors, the factor that all four programs showed as the most sensitive is the tire-roadway drag. Additionally, consistent with a reconstructionist’s intuition, is that the programs are sensitive to the initial (postimpact) velocities. However, the level of the sensitivities of the four programs to a given change in the same factor are different in many cases.</div><div class="htmlview paragraph">As compelling as the results are that show the largest sensitivities, the results show factors that some, or all, of the programs show little sensitivity. For example, for response using the <i>y</i>-coordinate and rotational displacement of the vehicle at rest, all four of the programs were relatively insensitive to changes in the lateral and longitudinal stiffnesses of the tires over the range selected.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Amphibious vehicles with both land and water navigation functions have extremely high application value in the military and civilian fields. In order to fully utilize the wheel driving force and ensure the smooth landing of the amphibious vehicle driven by four wheel hub motor, an acceleration slip regulation (ASR) is designed under the condition of landing from water. First, the road friction coefficient is identified based on the back propagation neural network (BPNN). Then, utilizing the improved Burckhardt model, the current optimal slip ratio is calculated from the identified road friction coefficient. Finally, the ASR under the condition of landing from water is designed based on radial basis function (RBF) single neuron adaptive PID control algorithm. By analyzing the process of amphibious vehicles transitioning from water to land, a typical working condition for amphibious vehicles landing is established, and a joint simulation is conducted using CarSim/Simulink. The simulation results indicate that, using the BPNN, the road friction coefficient of the typical working condition can be accurately identified. Compared to without ASR, after applying the ASR designed in this paper, the landing time of the amphibious vehicle is reduced by 7.5 s, and the final climbing velocity is increased by 7 km/h. After applying the ASR, the power performance of the amphibious vehicle during landing is improved, demonstrating that this ASR has significant practical application value.</div></div>

<div class="htmlview paragraph">This paper presents the engineering technology for the 1992 Corvette Acceleration Slip Regulation (ASR) system and Antilock Brake System (ABS).</div> <div class="htmlview paragraph">After the introduction of Bosch 2S anti-lock brakes in the 1986 Corvette, we experienced an improvement in vehicle stability and steerability during hard braking. The next challenging task was to improve the vehicle's stability during acceleration.</div> <div class="htmlview paragraph">The goal was to assist the driver of this high horse power front engine, rear wheel drive sports car on low coefficient surfaces. This goal was accomplished with the functional integration of engine torque management and brake intervention. This required functional integration of three subsystems: engine spark retard, throttle close down and brakes. This is the first application for a throttle close down device which provides driver feed back of slippery road conditions, through the accelerator pedal. The Bosch Corporation control strategies programmed into the electronic control unit (ECU), have enabled Corvette Engineering to enhance the vehicle acceleration and stability on a variety of road surfaces under difficult driving conditions. These control strategies were further optimized to provide balanced driving performances for winter, summer, fall and spring ambient conditions.</div>