This thesis investigates the use of an active anti-roll bar as a means of improving the handling of an off-road vehicle. The active anti-roll bar consists of a stiff anti-roll bar and a hydraulic actuator at the one end between the anti-roll bar and the rear axle of the vehicle. The system is designed so that the anti-roll bar can be preloaded in both directions by the actuator. The displacement of the hydraulic actuator is close loop controlled to be a function of the lateral acceleration of the vehicle, which is measured by an accelerometer. For this study, full vehicle simulations were done in ADAMS/View to predict the response of the proposed solutions. A Land Rover Defender 110 was used as the test vehicle to verify the results of the simulations. Constant radius tests and the severe double-lane-change manoeuvre, which are standard handling tests, were used to determine the vehicle’s handling performance. Handling performance was quantified by measuring the body roll angle during the manoeuvre and noting the maximum roll angle. The effect of the active anti-roll bar on ride comfort was measured by driving over Belgian paving at a constant speed. The results show that the proposed system reduces the body roll angle to zero up to a lateral acceleration of 0.4 g during steady state handling and provided a 74% improvement in maximum body roll angle during a double-lane-change-manoeuvre at 70 km/h. The system has no detrimental effect on the ride comfort of the vehicle. / Dissertation (MEng)--University of Pretoria, 2008. / Mechanical and Aeronautical Engineering / unrestricted

Vehicle dynamics development is strongly based on subjective assessments (SA) of vehicle prototypes, which is expensive and time consuming. Consequently, in the age of computer- aided engineering (CAE), there is a drive towards reducing this dependency on physical test- ing. However, computers are known for their remarkable processing capacity, not for their feelings. Therefore, before SA can be computed, it is required to properly understand the cor- relation between SA and objective metrics (OM), which can be calculated by simulations, and to understand how this knowledge can enable a more efficient and effective development process. The approach to this research was firstly to identify key OM and SA in vehicle dynamics, based on the multicollinearity of OM and of SA, and on interviews with expert drivers. Sec- ondly, linear regressions and artificial neural network (ANN) were used to identify the ranges of preferred OM that lead to good SA-ratings. This result is the base for objective require- ments, a must in effective vehicle dynamics development and verification. The main result of this doctoral thesis is the development of a method capable of predicting SA from combinations of key OM. Firstly, this method generates a classification map of ve- hicles solely based on their OM, which allows for a qualitative prediction of the steering feel of a new vehicle based on its position, and that of its neighbours, in the map. This prediction is enhanced with descriptive word-clouds, which summarizes in a few words the comments of expert test drivers to each vehicle in the map. Then, a second superimposed ANN displays the evolution of SA-ratings in the map, and therefore, allows one to forecast the SA-rating for the new vehicle. Moreover, this method has been used to analyse the effect of the tolerances of OM requirements, as well as to verify the previously identified preferred range of OM. This thesis focused on OM-SA correlations in summer conditions, but it also aimed to in- crease the effectiveness of vehicle dynamics development in general. For winter conditions, where objective testing is not yet mature, this research initiates the definition and identifica- tion of robust objective manoeuvres and OM. Experimental data were used together with CAE optimisations and ANOVA-analysis to optimise the manoeuvres, which were verified in a second experiment. To improve the quality and efficiency of SA, Volvo’s Moving Base Driving Simulator (MBDS) was validated for vehicle dynamics SA-ratings. Furthermore, a tablet-app to aid vehicle dynamics SA was developed and validated. Combined this research encompasses a comprehensive method for a more effective and ob- jective development process for vehicle dynamics. This has been done by increasing the un- derstanding of OM, SA and their relations, which enables more effective SA (key SA, MBDS, SA-app), facilitates objective requirements and therefore CAE development, identi- fies key OM and their preferred ranges, and which allow to predict SA solely based on OM. / <p>QC 20170223</p> / iCOMSA

Capturing what is going on and what may happen related to vehicle handling behaviour in cases of desired or non-desired actions and interventions has a crucial importance. Strategies implemented to improve vehicle stability or algorithms and control modules designed to compensate the non-desired effects on handling behavior may appear to be inadequate as the vehicle goes through uncountable experiences. The importance of understanding and introducing the possible sources of undesired effects which may be encountered throughout driving action cannot be underemphasized. One of the possibilities that may lead the driver face with unexpected results concerning vehicle&rsquo / s handling is suspension damper failure, which has not yet been dealt with adequately in the literature. The fast developing technology and consequently the expanding utilization of chassis electronics and electronic vehicle components make the investigation of damper failure phenomenon essential since reliability decreases by the continuously increasing introduction of electronic means. In this study, possible failure types of dampers including electrical failure are taken into account, their effects on vehicle stability under critical driving conditions are examined. Shortcomings and comments are made on criticality of failed damper and its failure point. This work as a result, constitutes a particular contribution to the literature in that it brings up a concrete knowledge to the stated research area.

Driving can provide independent and efficient mobility. However, according to the driving license directive (91/439/EEC) are persons with locomotor impairments are only allowed drive if their disabilities can be compensated. Compensation can be realised by vehicle adaptations. The directive provides meagre guidance on how vehicles should be adapted or how to verify that the compensatory requirements are fulfilled. This is a gap in the current process for licensing drivers with physical disabilities. Furthermore, the Swedish process from driver assessment to driver licensing and adaptation approval is complex, fragmented, and suffer from lack of communication between involved authorities. The objective of this thesis was to contribute to the development of a method to evaluate vehicle adaptations for driver with physical disabilities. The focus was on the evaluation of adaptations for steering, accelerating and braking. Three driving simulator experiments and one manoeuvre test with adapted vehicles were conducted. A group of drivers with tetraplegia driving with hand controls were compared to able-bodied drivers in the first experiment. Even if the drivers with tetraplegia had a longer brake reaction time they performed comparable to the able-bodied drivers. However, they spent more effort and were more tired in order to perform as well as the able-bodied drivers. It was concluded that the adaptation was not sufficient. An Adaptive Cruise Controller (ACC) was tested in the second experiment in order to find out if it could alleviate the load on drivers using hand controls. It was found that the ACC decreased the workload on the drivers. However, ACC systems need to be adjustable and better integrated. The results from the first two experiments were used to provide some guidelines for ACCsystems to be used by drivers with disabilities. The third experiment was preceded by a manoeuvre test with joystick controlled cars. The test revealed some problems, which were attributed to time lags, control interference, and lack of feedback. Four joystick designs were tested with a group of drivers with tetraplegia in the third experiment. It was concluded that time lags should be made similar to what is found in standard cars. Lateral and longitudinal control should be separated. Active feedback can improve vehicle control but should be individually adjusted. The experiments revealed that drivers with the same diagnose can be functionally very diverse. Thus, an adaptation evaluation should be made individually. Furthermore, the evaluation should include a manoeuvre test. Finally, it was concluded that the evaluation approach applied in the experiments was relevant but needs to be further developed.

The work presented in this thesis is devoted to the study of mechanism of tyre force generation and its influence on handling dynamics of ground vehicles. The main part of the work involves the development of tyre models for use under steady-state and transient operating conditions. The general capability of these models is assessedin a full vehicle simulation environment. The interaction between tyre and vehicle dynamics is critically evaluated and the observed vehicle behaviour is related to the inherent characteristics of different tyre models. In the field of steady-state tyre modelling, two versions of a numerical tyre model are developed. The modelling procedure is carried out in accordance with the viscoelastic properties of rubber, which influence the mechanical properties of the tyre structure and play a significant role in the determination of friction in the tyre contact patch. Whilst the initial simple version of the tyre model assumes a parabolic pressure distribution along the contact, a later more elaborate model employs a numerical method for the calculation of the actual normal pressure distribution. The changes in the pressure distribution as a result of variations in the rolling velocity and normal load influence mainly the levels of self-aligning moment, whilst the force characteristics remain practically unaffected. The adoption of a velocity dependent friction law explains the force generating behaviour of tyres at high sliding velocities. The analysis is extended to the area of transient tyre behaviour with the development of a tyre model appropriate for the study of transient friction force generation within the contact patch. The model incorporates viscoelasticity and inertial contributions, and incorporates a numerical stick-slip law. These characteristics are combined together for the successful simulation of transient friction force generation. The methodologies developed for the modelling of transient friction and steady-state tyre force generation are combined and further extended in order to create a generic transient tyre model. This final model incorporates a discretised flexible viscoelastic belt with inertia and a separate fully-dynamic discretised tread, also with inertia and damping, for the simulation of actual prevailing conditions in the contact patch. The generic tyre model appears to be capable of performing under a variety of operating conditions, including periodic excitations and transient inputs which extend to the non-linear range of tyre behaviour. For the evaluation of the influence of the aforementioned tyre models on the handling responses of a vehicle, a comprehensive vehicle model is developed, appropriate for use in handling simulations. The two versions of the steady-state models and the generic transient model are interfaced with the vehicle model, and the response of the vehicle to a step-steer manoeuvre is compared with that obtained using the Magic Formula tyre model. The comparison between the responses is facilitated by the definition of a new measure, defined as the non-dimensional yaw impulse. It is found that the transience involved in tyre behaviour may largely affect the response of a vehicle to a prescribed input.

Orientador: Franco Giuseppe Dedini / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-09T20:19:37Z (GMT). No. of bitstreams: 1 Silva_LudmilaCorreaAlkmine_M.pdf: 11763178 bytes, checksum: 949344e47dc2505f86cd5805376922d8 (MD5) Previous issue date: 2007 / Resumo: Neste trabalho foi desenvolvido um laboratório virtual para dinâmica veicular e modelagem do contato roda-piso que foi usado para a visualização do comportamento dinâmico de uma cadeira de rodas em diversas situações. Utilizando o ambiente Working Model 2Dâ para a integração das equações de movimento e visualização dos deslocamentos e movimentos associados, implementou-se modelos do contato roda-piso a partir da literatura de referência. Foram propostos sucessivamente quatro diferentes modelos do contato roda-piso, um modelo próprio para o controle da velocidade e aceleração, o modelo de Huston, a fórmula mágica e por último o modelo de Raheman. Todos esses modelos foram implementados, simulados e comparados entre si, por meio de imagens e gráficos obtidos. Todos os modelos se mostraram bastante confiáveis e suficientemente simples. No entanto, não existem dados confiáveis para os coeficientes destes modelos quando usados para a modelagem de rodas e ambientes inteiros como acontece em uma cadeira de rodas. Assim levou-se ao desenvolvimento de uma bancada experimental para a obtenção desses parâmetros / Abstract: In this work it was developed a virtual laboratory to vehicular dynamics and the modeling of the contact between ground and wheel that was used to visualize the dynamic behavior of the wheelchair in diverse situations. Using the Working Model 2D for the integration of the equations of motion and visualization of the displacements, the model of the contact between the ground and wheel had been implemented from the reference literature. Four different models of the contact between ground and wheel had been considered successively, a proper model for control of the speed and acceleration, the Huston model, the Magic Formula and then the Raheman model. All these models had been implemented simulated and compared each other by figures and graphs. All the models developed was sufficiently trustworthy and enough simple. However, trustworthy parameters do not exist for the coefficient of these models when used for the modeling of the wheelchair. So was developed an experiment to raise these parameters / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

<div>Indiana University–Purdue University Indianapolis student team Jaguar has been participating in the electric Formula SAE (FSAE) vehicle competitions in the past few years. There is an urgent need to develop a design tool for improving the performance of the vehicle. In this thesis, multibody dynamics (MBD) models have been developed which allow the student team to improve their vehicle design, while reducing the required time and actual testing costs. Although there were some studies about MBD analyses for vehicles in literature, a detailed modeling study of key parameters is still missing. Specifically, the effect of suspension system on the vehicle performance is not well studied. </div><div>The objective of the thesis is to develop an MBD based model to improve the FSAE vehicle’s performance. Based on the objective and knowledge gap, the following research tasks are proposed: (1) MBD modeling of current suspension systems; (2) Modification of suspension systems, and (3) Evaluation of performance of modified suspension systems. </div><div>The models for the front suspension system, rear suspension system, and full assembly are created, and a series of MBD analyses are conducted. The parameters of the vehicle by conducting virtual tests on the suspension model and overall vehicle model are studied. In this work, two main virtual tests are performed. First, parallel wheel travel test on suspension system, in which the individual suspension system is subject to equal force on both sides. The test helps understand the variation in stability parameters, such as camber angle, toe angle, motion ratio, and roll center location. Second, skid-pad test on full assembly of the vehicle. The test assists in understanding the vehicle’s behavior in constant radius cornering and the tire side slip angle variation, as it is one of the important parameters controlling alignment of the vehicle in this test.</div><div>Based on the vehicle’s dynamics knowledge obtained from the existing vehicle, a modified version of the FSAE vehicle is proposed, which can provide a better cornering performance with minimum upgrades and cost possible. Based on the results from the parallel wheel travel test and skid-pad test, the lateral load transfer method is used to control the vehicle slip, by making changes to the geometry of the vehicle and obtaining appropriate roll center height for both front and rear suspension system. The results show that the stiffness in front suspension system and rear suspension system are controlled by manipulating roll center height. This study has provided insightful understanding of the parameters and forces involved in suspension system and their variations in different events influencing vehicle stability. Moreover, the MBD approach developed in this work can be readily extended to other commercial vehicles and sports vehicles.</div><div><br></div>

This article presents transient handling analysis with a full-vehicle non-linear multi-body dynamic model, having 102 degrees of freedom. A transient cornering manoeuvre, with a constant steer angle and velocity has been undertaken. The effects of aerodynamic lift and drag forces have been included in the simulation tests. The vehicle handling characteristics with and without aerodynamic forces have been compared and various observations made. The aerodynamic forces have been predicted by a k¿1 model solution of the Navier¿Stokes equations for turbulent flow. The numerical predictions for the evaluation of aerodynamic lift coefficient agrees well with the scaled-down air tunnel experimental work, using hot-wire anemometry

Due to a recent number of undesired rollovers in the field for the studied vehicle, rollover mitigation strategies have been investigated and developed. This research begins with the study of the tire, as it is the single component on the vehicle responsible for generating all of the non-inertial forces to direct the motion of the vehicle. Tire force and moment behavior has been researched extensively and several accurate tire models exist. However, not much research has been performed on off-road tire models. This research develops an off-road tire model for the studied vehicle by first using data from rolling road testing to develop a Pacejka Magic Formula tire model and then extending it to off-road surfaces through the use of scaling factors. The scaling factors are multipliers in the Magic Formula that describe how different aspects of the force and moment curves scale when the tire is driven on different surfaces. Scaling factors for dirt and gravel driving surfaces were obtained by using an existing portable tire test rig to perform force and moment tests on a passenger tire driven on these surfaces. The off-road tire model was then used as a basis for developing control algorithms to prevent vehicle rollover on off-road terrain. Specifically, a direct yaw control (DYC) algorithm based on Lyapunov direct method and an emergency roll control (ERC) algorithm based on a rollover coefficient were developed. Emergency evasive maneuvers were performed in a simulation environment on the studied vehicle driven on dry asphalt, dirt, and gravel for the controlled and uncontrolled cases. Results show that the proposed control algorithms significantly improve vehicle stability and prevent rollover on a variety of driving surfaces. / Master of Science

The thesis presents an intermediate modelling approach to study transient behaviour of vehicle systems, with emphasis put on simplified yet accurate representation of important system elements. A representative non-linear vehicle model is developed in MA TLAB/Simulink environment, where non-linear characteristics of tyre, suspension and braking system are included to capture the dynamic behaviour of a vehicle under transient conditions. The novel aspect of this work is the application of a representative full vehicle-tyre-ABS integrated set-up to study the complicated interaction between tyre and anti-lock braking, under a range of demanding operating conditions, including combined cornering and braking. The modelling methodology involves development of low end vehicle models, based on the Newton-Euler formulation. Subsequently, an intermediate vehicle model is devised, where more details are incorporated such as additional DOF to capture the sprung mass motion in space, along with its non-linear interactions with the un-sprung masses, large angle effects, kinematics of steering/wheels and an appropriate tyre model suitable for transient manoeuvres. Particular attention is paid to the suspension system modelling, through inclusion of non-linear effects in springs, dampers, bump-stops, and anti-roll bars, along with the jacking and anti-dive effects using the virtual work method. The model also incorporates a hydraulic brake model, based on the reduced order brake system dynamics for realistic simulation of the braking manoeuvres. A complex multi-body ADAMS/Chassis model, with much greater level of detail, has also been established to extensively compare and enhance the realistic behaviour of the intermediate vehicle model. During the simulation exercise, the intermediate vehicle model has shown good agreement with the complex ADAMS model, thus justifying the accurate representation of vehicle.non-linear characteristics, particularly the suspension system. The realistic behaviour of the vehicle model is further ascertained with a reliable GPS enabled test vehicle, by performing number of manoeuvres on test tracks, including combined cornering and braking. A representative 4-channel conventional ABS system is modelled and integrated in the intermediate vehicle model. The ABS adopts generic peak seeking approach, employing wheel deceleration and brake slip as control variables. External braking inputs, in form of stepped pressure pulses, are also separately used to represent the transient braking system dynamics. In the current work, different transient tyre models based on the single point contact approach and using Magic Formula steady-state characteristics are applied, while studying the influence of their dynamic behaviour on the ABS system. By employing a representative ABS system in a multi-body vehicle model and considering the particularly demanding situation of combined braking I cornering, it is shown that the models which are adequate for pure braking might struggle when the complicated full vehicle dynamics are excited. It is shown that the first order relaxation length approach may not be sufficient to fully satisfy the requirements of an ABS braking, especially if the relaxation length is not modelled as a variable dependent on tyre slip. In comparison, the modelling approach, where the carcass compliances and contact patch properties are explicitly represented, can handle the oscillatory tyre behaviour associated with ABS braking, in a far more accurate manner. In comparison to the earlier studies, which were mostly conducted for straight-line braking, this thesis stresses the fact that the tyre behaviour can be influenced by the complex interaction of handling and braking, and hence the effect should be captured while investigating or evaluating the performance of a tyre model in relation with ABS simulation.