Vehicle Dynamic Behavior Research Articles

In Situ Measurement of Discomfort Curves for Seated Subjects in a Car on the Four-Post Rig

The aim of this study is to measure and quantify perceived intensity of discomfort due to vibration in a vehicle in situ considering complete vehicle dynamic behaviour. The shaker table based discomfort curves or the road test results may not accurately and universally indicate the true level of human discomfort in a vehicle. A new experimental method, using a seated human in a car on the four-post rig simulator, is proposed to quantify discomfort. The intensity of perception to vibration decreased with decreasing input and increasing frequency; the rate of change is different from the published literature; the difference is large for angular modes of inputs. Vehicle dynamic response is used to inform and analyse the results. The repeatability of the method and the fact that they are in situ measurements may eventually help reduce reliance on the road tests. Furthermore, discomfort curves obtained, subsequently, can be used in predictive models.

Optimal Roll Center Height of Front McPherson Suspension System for a Conceptual Class A Vehicle

In this paper, the effects of roll center height of McPherson suspension mechanism on dynamic behaviour of a vehicle are first studied, and then the optimum location of roll center of this suspension system is determined for a conceptual Class A vehicle. ADAMS/Car software was used for the analysis of vehicle dynamic behaviour in different positions of suspension roll center. Next, optimization process has been done using ADAMS/Insight. Results show significant effects of roll center location on body roll angle, body roll rate and steering response. Also, the contradiction between body roll and steering response can be observed.

Fault classification method for the driving safety of electrified vehicles

A fault classification method is proposed which has been applied to an electric vehicle. Potential faults in the different subsystems that can affect the vehicle directional stability were collected in a failure mode and effect analysis. Similar driveline faults were grouped together if they resembled each other with respect to their influence on the vehicle dynamic behaviour. The faults were physically modelled in a simulation environment before they were induced in a detailed vehicle model under normal driving conditions. A special focus was placed on faults in the driveline of electric vehicles employing in-wheel motors of the permanent magnet type. Several failures caused by mechanical and other faults were analysed as well. The fault classification method consists of a controllability ranking developed according to the functional safety standard ISO 26262. The controllability of a fault was determined with three parameters covering the influence of the longitudinal, lateral and yaw motion of the vehicle. The simulation results were analysed and the faults were classified according to their controllability using the proposed method. It was shown that the controllability decreased specifically with increasing lateral acceleration and increasing speed. The results for the electric driveline faults show that this trend cannot be generalised for all the faults, as the controllability deteriorated for some faults during manoeuvres with low lateral acceleration and low speed. The proposed method is generic and can be applied to various other types of road vehicles and faults.

Fully Equipped Dynamic Model of a Bus

Nowadays, the time to market a new vehicle is crucial for every company as it is easier to meet the customers’ needs and expectations. However, designing a new vehicle is a long process which needs to take into account different performances. The most difficult is to predict a dynamic behavior of a vehicle especially when such a big vehicles as urban buses are considered. Therefore, there is a necessity to use a virtual model to investigate different performances. However, there is a lack of urban bus models that can fully reflect a dynamic behavior of the bus. This paper presents a fully equipped urban bus model which can be used to study a dynamic behavior of such vehicles. The model is based on innovative technique called cosimulation, which connects different modeling techniques (3D and 1D). Such a technique allows performing different analyses that require small deformations and large translations and rotations in shorter time and automatic way. The work has been carried out in a project EUREKA CHASING.

The Role of Tire Size Over the Fatigue Damage Accumulation in Vehicle Bodies

One of the most important components related to vehicle dynamics is the tire and wheel set. According to their dimensions (diameter, height, width, design) the vehicle dynamic behavior and driving comfort are seriously affected. Besides these aspects, the wheel/tire configuration has a main role over vehicle design and style. Nowadays, there is a design strategy which main feature is the increase of wheel diameter, causing the reduction of the tire side profile (tire height). After the increase of the wheel size, the total dynamic and static diameter of the whole set must be the same, causing the previous mentioned tire height reduction.In this work we investigate concerning the fatigue damage accumulation over light passenger vehicle body, related to the changes in the wheel/tire sizes. The vehicles were instrumented with strain gages in order to collect the stress levels acting at several areas of the vehicle body. These measurements were performed with a wide range of wheel/tire sizes in order to verify the importance of this component over structural integrity. The increase of the wheel size (and therefore decrease in tire height) has a significant role in the stress levels acting over the vehicle body, causing a higher fatigue damage accumulation. These new stress levels must be considered during the dimensioning of the vehicle components with higher wheel dimensions.

Vehicle dynamic behaviours crossing cat-eye reflectors

Cat-eye reflectors are used in the last few years to calm down with the demand of road flow especially local and domestic roads. However, it is normally distributed transversally to vehicle direction of motion. The aim of this study is to investigate the effect of cat-eye reflector configuration on the vehicle dynamic behaviour. This study is based on a quarter car model of four wheels independent suspension system. Vehicle vertical body acceleration, tyre dynamic load and suspension working space are calculated while the vehicle is crossing cat-eye reflectors at different speeds. Also, the case of common circular hump is investigated and compared with cat eye hump. The results indicate that the dynamic behaviour of the vehicle crossing cat-eye hump is contrary to what should be the hump design considerations. As the vehicle crossing cat-eye hump, vehicle vertical acceleration has higher values at low vehicle speed and with the increase of vehicle speed, the vehicle vertical acceleration devolves to lower values. On the contrary, using common circular hump has reasonable ride comfort at low vehicle speeds; when the vehicle speed increases the ride comfort becomes worse.

Development of a Software in the Loop Environment for Automotive Powertrain Systems

In the last years the interest for hybrid vehicles increased mainly for environmental reasons. The dynamic behavior of a vehicle is then influenced by the interaction between the engine and the hybrid system. The final goal of the paper is to realize a software in the loop environment which can be utilized for the development of control strategies for hybrid vehicles.This paper presents the implementation of a simplified engine-driveline model to complete an existing vehicle dynamic model. The engine model is based on maps which are expressed as function of engine speed and load request. Particular care is devoted to the clutch model which allows describing both the situations of engaged and disengaged clutch. The driveline model also permits to change the transmission ratio between engine and wheels depending on the selected gear. The model parts are integrated, taking into account the requirement to use the model in real time simulations, coupling to the engine-driveline with a pre-existing vehicle dynamics model by means of the vehicle driving wheels. The complete vehicle-engine model is used to evaluate the differences in vehicle dynamic behavior when additional masses are added to the vehicle and the position of vehicle center of gravity is changed.

Simulation and experimental evaluations on the performance of pneumatically actuated active roll control suspension system for improving vehicle lateral dynamics performance

This paper presents the derivation of a full vehicle model which consists of ride, handling and tyre subsystems to study vehicle dynamics behaviour in the lateral direction. The full vehicle model is then validated experimentally using an instrumented experimental vehicle based on steering wheel input from the driver. Three types of vehicle dynamics test were performed for model validation, namely step steer, slalom and double lane change tests. The validation results show that the behaviours of the model are similar to the real vehicle with acceptable error. An Active Roll Control (ARC) suspension system was developed using the validated full vehicle model to reduce unwanted vehicle motions during steering input manoeuvres such as body roll angle, body roll rate, vertical acceleration of the body and body heave. The proposed controller for the ARC system is a combination of Proportional-Integral-Derivative (PID) control with roll moment rejection loop. The results of the study show that the proposed control structure significantly improves the dynamics performance of the vehicle during step steer, slalom and double lane change manoeuvres compared with a passive vehicle system. The additional roll moment rejection loop is found to be able to further improve the performance of the PID ARC system. The effectiveness of the ARC system with the proposed control was also proven experimentally using the instrumented experimental vehicle.

Motion-mode energy method for vehicle dynamics analysis and control

Vehicle motion and vibration control is a fundamental motivation for the development of advanced vehicle suspension systems. In a vehicle-fixed coordinate system, the relative motions of the vehicle between body and wheel can be classified into several dynamic stages based on energy intensity, and can be decomposed into sets of uncoupled motion-modes according to modal parameters. Vehicle motions are coupled, but motion-modes are orthogonal. By detecting and controlling the predominating vehicle motion-mode, the system cost and energy consumption of active suspensions could be reduced. A motion-mode energy method (MEM) is presented in this paper to quantify the energy contribution of each motion-mode to vehicle dynamics in real time. The control of motion-modes is prioritised according to the level of motion-mode energy. Simulation results on a 10 degree-of-freedom nonlinear full-car model with the magic-formula tyre model illustrate the effectiveness of the proposed MEM. The contribution of each motion-mode to the vehicle's dynamic behaviour is analysed under different excitation inputs from road irregularities, directional manoeuvres and braking. With the identified dominant motion-mode, novel cost-effective suspension systems, such as active reconfigurable hydraulically interconnected suspension, can possibly be used to control full-car motions with reduced energy consumption. Finally, discussion, conclusions and suggestions for future work are provided.

Tyre–road grip coefficient assessment. Part 1: off-line methodology using multibody dynamic simulation and genetic algorithms

A key factor to understand the vehicle dynamic behaviour is to know as accurately as possible the interaction that occurs between the tyre and the road, since it depends on many factors that influence the dynamic response of the vehicle. This paper aims to develop a methodology in order to characterise the tyre–road behaviour, applying it to obtain the tyre–road grip coefficient. This methodology is based on the use of dynamic simulation of a virtual model, integrated into a genetic algorithm that identifies the tyre–road friction coefficient in order to adjust the response obtained by simulation to real data. The numerical model was developed in collaboration with SEAT Technical Centre and it was implemented in multibody dynamic simulation software Adams®, from MSC®.

Analytic Design of Active Safety Systems for Vehicular Ad hoc Networks

We analytically study parameter design for safety applications in Vehicular Ad hoc Networks. Our goal is to fill in the current gap between purely traffic-based studies that fail to account for the non-idealities of communications, and communications-based ones which neglect the application needs of the system. Initially and by studying the dynamic behavior of vehicles we address the delay requirement of the safety application. We then derive the delay-bounded packet success probability of three Media Access Control (MAC) schemes proposed for the dissemination of periodic safety messages. By simultaneously accounting for multi-user interference and propagation effects such as path loss and fading, we determine the optimal transmission rate, channel access probability, and when pertinent, carrier sensing range of those schemes that satisfy the delay requirement at a target success probability. Of our findings is that the optimal transmission rate varies only with the path loss exponent, irrespective of the MAC scheme used. Also, the optimal communications parameters that minimize the maximum expected collision probability in a chain of vehicles is only dependent on the human factors (perception-reaction time and deceleration behavior) and highway characteristics (number of lanes and path loss exponent) and hence do not have to vary with traffic conditions.

Adaptive optimal control allocation using Lagrangian neural networks for stability control of a 4WS–4WD electric vehicle

This study involves a layered vehicle dynamics control system, which is composed of an adaptive optimal control allocation method using Lagrangian neural networks for optimal distribution of tyre forces and the sliding mode yaw moment observer for robust control of yaw dynamics. The proposed optimal control allocation method eliminates the requirement of solving optimization problem in every time step and it is a convergent and stability guaranteed solution for the optimal tyre force distribution problem. The aim in the sliding mode yaw moment observer is to force the vehicle to track a reference vehicle dynamic behaviour by estimating the equivalent input extended disturbance, which is the required stabilizing virtual yaw moment. The proposed layered stability control scheme has been tested on a four-wheel drive–four-wheel steer electric Fiat Doblo Van, which is modelled in CarSim. Both the sliding mode disturbance observer and the optimal control allocation methods are the first known applications to the stability control problem of road vehicles.

Study on safety boundary for high-speed train running in severe environments

This article reviews some important published papers regarding the discussions on the mechanism and the modelling of trains operating in severe environments which are originally defined. A few important derailment criteria are briefly discussed. A study strategy of the safety operation boundaries of high-speed trains operating in the severe environments is first put forward. In the strategy, the safety operation boundaries are defined as a number of separatrices which clearly indicate the safety operation area, warning area and derailment occurring area of a high-speed vehicle in operation. The defined separatrices are the limit surface functions of the key factors influencing the vehicle dynamic behaviour and its derailment. They are found through numerical simulation by using an advanced dynamics model for vehicle/track interaction and the derailment criteria. In order to fully understand the present strategy, a detailed numerical example of a high-speed vehicle passing over a buckled track is discussed. The given results clearly indicate the effects of the key factors on the wheel/rail normal forces, the derailment criteria limits and the vehicle derailment boundary.

Sensitivity analysis to assess the influence of the inertial properties of railway vehicle bodies on the vehicle's dynamic behaviour

A sensitivity analysis has been performed to assess the influence of the inertial properties of railway vehicles on their dynamic behaviour. To do this, 216 dynamic simulations were performed modifying, one at a time, the masses, moments of inertia and heights of the centre of gravity of the carbody, the bogie and the wheelset. Three values were assigned to each parameter, corresponding to the percentiles 10, 50 and 90 of a data set stored in a database of railway vehicles. After processing the results of these simulations, the analysed parameters were sorted by increasing influence. It was also found which of these parameters could be estimated with a lesser degree of accuracy for future simulations without appreciably affecting the simulation results. In general terms, it was concluded that the most sensitive inertial properties are the mass and the vertical moment of inertia, and the least sensitive ones the longitudinal and lateral moments of inertia.

Assessment of the influence of the elastic properties of rail vehicle suspensions on safety, ride quality and track fatigue

A sensitivity analysis has been performed to assess the influence of the elastic properties of railway vehicle suspensions on the vehicle dynamic behaviour. To do this, 144 dynamic simulations were performed modifying, one at a time, the stiffness and damping coefficients, of the primary and secondary suspensions. Three values were assigned to each parameter, corresponding to the percentiles 10, 50 and 90 of a data set stored in a database of railway vehicles. After processing the results of these simulations, the analysed parameters were sorted by increasing influence. It was also found which of these parameters could be estimated with a lesser degree of accuracy in future simulations without appreciably affecting the simulation results. In general terms, it was concluded that the highest influences were found for the longitudinal stiffness and the lateral stiffness of the primary suspension, and the lowest influences for the vertical stiffness and the vertical damping of the primary suspension, with the parameters of the secondary suspension showing intermediate influences between them.

Influence of the track quality and of the properties of the wheel–rail rolling contact on vehicle dynamics

This work describes an analytical approach to determine what degree of accuracy is required in the definition of the rail vehicle models used for dynamic simulations. This way it would be possible to know in advance how the results of simulations may be altered due to the existence of errors in the creation of rolling stock models, whilst also identifying their critical parameters. This would make it possible to maximise the time available to enhance dynamic analysis and focus efforts on factors that are strictly necessary. In particular, the parameters related both to the track quality and to the rolling contact were considered in this study. With this aim, a sensitivity analysis was performed to assess their influence on the vehicle dynamic behaviour. To do this, 72 dynamic simulations were performed modifying, one at a time, the track quality, the wheel–rail friction coefficient and the equivalent conicity of both new and worn wheels. Three values were assigned to each parameter, and two wear states were considered for each type of wheel, one for new wheels and another one for reprofiled wheels. After processing the results of these simulations, it was concluded that all the parameters considered show very high influence, though the friction coefficient shows the highest influence. Therefore, it is recommended to undertake any future simulation job with measured track geometry and track irregularities, measured wheel profiles and normative values of the wheel–rail friction coefficient.

Optimum Design of 1st Gear Ratio for 4WD Vehicles Based on Vehicle Dynamic Behaviour

This paper presents an approach that allows optimizing gear ratio and vehicle dimension to achieve optimum gear transmission. Therefore, augmented Lagrangian multiplier method, defined as classical method, is utilized to find the optimum gear ratios and the corresponding number of gear teeth applied to all epicyclical gears. The new method is able to calculate and also to optimize the gear ratio based on dynamics of 4WD vehicles. Therefore, 4WD vehicles dynamic equations are employed assuming that the rear wheels or the front wheels are at the point of slip. In addition, a genetic algorithm is modified to preserve feasibility of the encountered solutions. The basic dimension of a sample commercial vehicle (2009 hummer H3 4dr AWD SUV) and its gearbox are optimized, and then the effects of changing slip angle, wheel base, and engine torque on optimum vehicle dimension are analyzed.

HYBRID MODELLING OF AN URBAN BUS

Sophisticated virtual prototyping methods have become a standard in the modern vehicle design process. Unfortunately, in many cases automobile manufacturers (in particular bus manufacturers) still do not take advantage of numerical de­sign techniques, basing instead on intuition and experience. In this paper hybrid modelling of an urban bus is presented. A hybrid bus model links different types of modelling that can be used to perform a wide range of virtual analyses of vehicle static and dynamic behaviour. The major objective of development and usage of a complex model is to reduce a time and cost of vehicle design process improving vehicle quality at the same time. The main advantage instead is a possibility to exploit a model for different performances of vehicle subsystems. A hybrid model representing real vehi­cle behaviour consists of three modelling techniques commonly used in automotive industry: multibody modelling, finite element modelling and multi- port (block) modelling. A full model has been developed via commercial software which ensures its availability among automotive engineers.

Numerical optimisation methods applied to the concurrent problem of vehicle ride and handling

This text presents a new proposal for an overall ride and handling metric to be used to optimise vehicle performance through concurrent simulation models. The proposed metric has the intention to cover simultaneously the most relevant aspects of a passenger vehicle dynamic behaviour. The individual models for ride and handling have been validated against physical measurements in order to assure a reliable output. A numerical optimisation method is used to simultaneously evaluate the complete vehicle dynamic performance related to the single overall metric. The results show an effective way to improve the vehicle performance based on this new proposed metric, with gains in terms of reduction in development time and cost for new projects.

New and renewed developments in automotive control

There are currently new and renewed automotive trends that are made possible by new sensors, models, and methodologies. There is renewed interest in interpretation of in-cylinder phenomena, and for engines the approach of mean value modeling is maturing so that established modeling blocks can be combined in many new configurations like e.g. multiple turbo systems. For the vehicle as a whole there has been a dramatic development in experimental possibilities, since there now exist cost effective vehicle dynamometers and sensors for vehicle dynamics behavior. This has increased activities in realistic driving cycles and in optimal maneuvers. A final aspect is the integration with transportation and smart houses, which leads to overall city planning.