Engineers of off-road equipment, on-road vehicles, pavement, and tires must assess the roughness of a terrain surface for the design of their products. The International Roughness Index (IRI), a standardized means of assessing longitudinal road roughness, quantifies roughness based on the average suspension travel for a particular vehicle at a prescribed speed. The Discrete Roughness Index (DRI) developed in this work address fundamental limitations of the IRI. Specifically, the DRI is calculated for each discretely measured location along a terrain surface and is applicable to vehicles traveling at varying speeds and using parameters other than the Golden Quarter-Car on which the IRI is based. The development of the DRI begins with a consistent discretization of the terrain surface, vehicle response, and the IRI. Next the Fractional Response Coefficient is developed, the properties of which are critical in the development of the DRI. The DRI is developed and its properties are discussed through theory and simulation of the ASTM E1926-08 profile. One important property of the average DRI is that it converges to the IRI as the distance between sampled points becomes smaller, for the particular case when the Golden Quarter-Car model is simulated at 80 kph. The DRI is not an alternative to the standard IRI, therefore, but a widely applicable roughness measure of which the standard IRI is a single specialized application. / Master of Science

Este trabalho apresenta um estudo sobre o comportamento de sistemas de pesagem em movimento baseados em plataformas comumente utilizadas no Brasil. Parâmetros relevantes nesse comportamento são modelados: rugosidade aleatória da pista, dinâmica vertical do veículo e sua velocidade, desnível entre a pista e plataforma e dinâmica da plataforma. Duas classes de veículos são simuladas trafegando a diferentes velocidades e sendo pesados utilizando uma proposta de modelo de plataforma rígida e uma proposta de plataforma flexível. As forças de reação do solo e históricos de aceleração em vários GDL são registrados a fim de obter a carga estática por eixo e os erros nas estimativas do peso para o modelo de plataforma rígida. Já para o modelo de plataforma flexível, as forças de reação servem de entrada no modelo de elemento finitos de viga Euler-Bernoulli com consideração da área de contato do pneu através de um trem de cargas. Conclusões relacionadas à redução da precisão do sistema com o aumento da velocidade do veículo são confirmadas, embora importantes conclusões não tão óbvias sobre a importância da dinâmica do veículo, do nível de rugosidade da pista, da altura do degrau pista-plataforma e da dinâmica da plataforma de pesagem são ressaltadas. / This work proposes a numerical study on the behavior of weigh-in-motion systems based on load platforms useful in Brazil. Some important parameters that may control this behavior that are modeled are random road roughness, vehicle vertical dynamics, vehicle speed, load platform step’s height to the road and platform dynamics. Two vehicles types are modelled travelling at different speeds and being weighted using a rigid platform proposal and another proposal with a flexible platform. Ground reaction force and acceleration time history on several degree-of-freedom are recorded in order to obtain the static load per axis and the corresponding estimated errors for the rigid platform model. For the flexible platform model, the reaction forces serve as inputs into the Euler-Bernoulli finite element model with consideration of the contact area of the tire by train of loads. Some usual conclusions related to the reduction in the accuracy of the measuring system with increased vehicle speed are confirmed in the numerical study, although important conclusions not so obvious concerning the importance of road roughness, vehicle vertical dynamics, and vehicle speed, load platform step’s height to the road and platform dynamics are highlighted.

Off-road and racing motorcycles require a particular setup of the suspension to improve the comfort and the safety of the rider. Further, due to ground unevenness, off-road motorcycle suspensions usually experience extreme and erratic excursions in performing their function. In this regard, the adoption of nonlinear devices, such as progressive springs and hydro pneumatic shock absorbers, can help limiting both the acceleration experienced by the sprung mass and the excursions of the suspensions. For dynamic analysis purposes, this option involves the solution of the nonlinear differential equations that govern the motion of the motorcycle, which is excited by the stochastic road ground profile. In this study a 4 degrees-of-freedom (4-DOF) nonlinear motorcycle model is considered. The model involves suspension elements with asymmetric behaviour. Further, it is assumed that the motorcycle is exposed to loading of a stochastic nature as it moves with a specified speed over a road profile defined by a particular power spectrum. It is shown that a meaningful analysis of the motorcycle response can be conducted by using the technique of statistical linearization. The validity of the proposed approach is established by comparison with results from pertinent Monte Carlo studies. In this context the applicability of auto-regressive (AR) filters for efficient implementation of the Monte Carlo simulation is pointed out. The advantages of these methods for the synthesis of excitation signals from a given power spectrum, are shown by comparison with other methods. It is shown that the statistical linearization method allows the analysis of multi-degree-of-freedom (M-DOF) systems that present strong nonlinearities, exceeding other nonlinear analysis methods in both accuracy and applicability. It is expected that the proposed approaches, can be used for a variety of parameter/ride quality studies and as preliminary design tool by the motorcycle industry.

Este trabalho apresenta um estudo sobre o comportamento de sistemas de pesagem em movimento baseados em plataformas comumente utilizadas no Brasil. Parâmetros relevantes nesse comportamento são modelados: rugosidade aleatória da pista, dinâmica vertical do veículo e sua velocidade, desnível entre a pista e plataforma e dinâmica da plataforma. Duas classes de veículos são simuladas trafegando a diferentes velocidades e sendo pesados utilizando uma proposta de modelo de plataforma rígida e uma proposta de plataforma flexível. As forças de reação do solo e históricos de aceleração em vários GDL são registrados a fim de obter a carga estática por eixo e os erros nas estimativas do peso para o modelo de plataforma rígida. Já para o modelo de plataforma flexível, as forças de reação servem de entrada no modelo de elemento finitos de viga Euler-Bernoulli com consideração da área de contato do pneu através de um trem de cargas. Conclusões relacionadas à redução da precisão do sistema com o aumento da velocidade do veículo são confirmadas, embora importantes conclusões não tão óbvias sobre a importância da dinâmica do veículo, do nível de rugosidade da pista, da altura do degrau pista-plataforma e da dinâmica da plataforma de pesagem são ressaltadas. / This work proposes a numerical study on the behavior of weigh-in-motion systems based on load platforms useful in Brazil. Some important parameters that may control this behavior that are modeled are random road roughness, vehicle vertical dynamics, vehicle speed, load platform step’s height to the road and platform dynamics. Two vehicles types are modelled travelling at different speeds and being weighted using a rigid platform proposal and another proposal with a flexible platform. Ground reaction force and acceleration time history on several degree-of-freedom are recorded in order to obtain the static load per axis and the corresponding estimated errors for the rigid platform model. For the flexible platform model, the reaction forces serve as inputs into the Euler-Bernoulli finite element model with consideration of the contact area of the tire by train of loads. Some usual conclusions related to the reduction in the accuracy of the measuring system with increased vehicle speed are confirmed in the numerical study, although important conclusions not so obvious concerning the importance of road roughness, vehicle vertical dynamics, and vehicle speed, load platform step’s height to the road and platform dynamics are highlighted.

Este trabalho apresenta um estudo sobre o comportamento de sistemas de pesagem em movimento baseados em plataformas comumente utilizadas no Brasil. Parâmetros relevantes nesse comportamento são modelados: rugosidade aleatória da pista, dinâmica vertical do veículo e sua velocidade, desnível entre a pista e plataforma e dinâmica da plataforma. Duas classes de veículos são simuladas trafegando a diferentes velocidades e sendo pesados utilizando uma proposta de modelo de plataforma rígida e uma proposta de plataforma flexível. As forças de reação do solo e históricos de aceleração em vários GDL são registrados a fim de obter a carga estática por eixo e os erros nas estimativas do peso para o modelo de plataforma rígida. Já para o modelo de plataforma flexível, as forças de reação servem de entrada no modelo de elemento finitos de viga Euler-Bernoulli com consideração da área de contato do pneu através de um trem de cargas. Conclusões relacionadas à redução da precisão do sistema com o aumento da velocidade do veículo são confirmadas, embora importantes conclusões não tão óbvias sobre a importância da dinâmica do veículo, do nível de rugosidade da pista, da altura do degrau pista-plataforma e da dinâmica da plataforma de pesagem são ressaltadas. / This work proposes a numerical study on the behavior of weigh-in-motion systems based on load platforms useful in Brazil. Some important parameters that may control this behavior that are modeled are random road roughness, vehicle vertical dynamics, vehicle speed, load platform step’s height to the road and platform dynamics. Two vehicles types are modelled travelling at different speeds and being weighted using a rigid platform proposal and another proposal with a flexible platform. Ground reaction force and acceleration time history on several degree-of-freedom are recorded in order to obtain the static load per axis and the corresponding estimated errors for the rigid platform model. For the flexible platform model, the reaction forces serve as inputs into the Euler-Bernoulli finite element model with consideration of the contact area of the tire by train of loads. Some usual conclusions related to the reduction in the accuracy of the measuring system with increased vehicle speed are confirmed in the numerical study, although important conclusions not so obvious concerning the importance of road roughness, vehicle vertical dynamics, and vehicle speed, load platform step’s height to the road and platform dynamics are highlighted.

Road roughness is the primary source of vehicle vibrations. This thesis investigates model-based methods for estimating road roughness in terms of the International Roughness Index (IRI) by measuring the chassis vibrations of the vehicle. This can provide NIRA Dynamics AB with a cost-effective pavement monitoring solution. Initially, system identification is performed on a physical car to estimate model parameters that reflect reality. Subsequently, two model-based IRI estimation methods are developed. One method relies on a transfer function between vertical chassis vibrations and the IRI according to a quarter-car model. The second method aims first to estimate the longitudinal road profile using a Kalman filter, and then calculate the IRI values from the estimated profile. This method can be implemented computationally efficiently and also offers the possibility of estimating the IRI using lateral vibrations. Both methods are validated using real-world data, and their performance is similar when using vertical vibrations, with the IRI estimation error’s standard deviation being roughly 10% to 20% of the reference value. However, the results are considerably worse when the estimation is purely based on lateral vibrations, indicating that lateral vibrations are not feasible for model-based IRI estimation, and the reasons for this are discussed.

Today, Sport Utility Vehicles are marketed as both on-road and off-road vehicles. This results in a compromise when designing the suspension of the vehicle. If the suspension characteristics are fixed, the vehicle cannot have good handling capabilities on highways and good ride comfort over rough terrain. The rollover propensity of this type of vehicle compared to normal cars is high because it has a combination of a high centre of gravity and a softer suspension. The 4 State Semi-active Suspension System (4S4) that can switch between two discrete spring characteristics as well as two discrete damper characteristics, has been proven to overcome this compromise. The soft suspension setting (soft spring and low damping) is used for ride comfort, while the hard suspension setting (stiff spring and high damping) is used for handling. The following question arises: when is which setting most appropriate? The two main contributing factors are the terrain profile and the driver’s actions. Ride comfort is primarily dependant on the terrain that the vehicle is travelling over. If the terrain can be identified, certain driving styles can be expected for that specific environment. The terrains range from rough and uncomfortable to smooth with high speed manoeuvring. Terrain classification methods are proposed and tested with measured data from the test vehicle on known terrain types. Good results were obtained from the terrain classification methods. Five terrain types were accurately identified from over an hour’s worth of vehicle testing. Handling manoeuvres happen unexpectedly, often to avoid an accident. To improve the handling and therefore safety of the vehicle, the 4S4 can be switched to the hard suspension setting, which results in a reduced body roll angle. This decision should be made quickly with the occupants’ safety as the priority. Methods were investigated that will determine when to switch the suspension to the handling mode based on the kinematics of the vehicle. The switching strategies proposed in this study have the potential, with a little refinement, to make the ride versus handling decision correctly. Copyright 2007, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Bester, R 2007, The ride comfort versus handling decision for off-road vehicles, MEng dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-10252007-111611 / > / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2007. / Mechanical and Aeronautical Engineering / unrestricted

The diploma thesis focuses especially on a design of a way for evaluating roughness in road profile, which affects driving characteristics of a car and a ride. In the theoretical part of the thesis are mentioned the most used methods and tools for road roughness analysis in the world. For the purposes of this thesis an experimental measuring were undertaken in order to obtain data for the own design of a road profile analysing system.

Mine haul road maintenance is traditionally done at scheduled intervals or after regular inspection. Both these methods can lead to unwarranted expenditure, either through over-maintaining the road, or failure to recognise significant deterioration, resulting in an increase in vehicle operating costs. Predictive maintenance management models for unpaved roads have been developed in recent years. These methods work well in a trivial environment where variables such as traffic volume can be predicted. However, many mining systems are too complex for such models to be effective. This work investigates the possibility of using haul truck response to aid haul road maintenance management. The approach adopted for the study was twofold: Firstly, can truck response data be used to recognise specific road defects, in terms of location, type and size? This is important since different defect types require different road maintenance strategies. Secondly, can road roughness be measured on a qualitative basis? With the emphasis on road defect reconstruction, a mathematical modelling approach was adopted. The truck was characterised in terms of its suspension and tyre properties. Dynamic truck response data was acquired during field measurements in which the vehicle was driven over defects of known dimensions. With these data sets available, mathematical modelling and simulation was possible. Quarter vehicle and seven degree of freedom vehicle models played a vital role in this work by laying a foundation in the use of haul truck response for the purpose of road defect reconstruction. A modelling methodology that is based on dynamic equilibrium of an independent front unsprung mass of the truck is proposed in which the vertical dynamic tyre force and eventually the road geometry is calculated. It is shown that defects can be reconstructed from measured truck response data with an accuracy sufficient to fulfil the requirements of defect recognition for road maintenance management purposes. Secondly, a preliminary investigation into the qualitative assessment of road condition via truck response measurements was conducted. The inherent response properties of the truck pertaining to road roughness measurement were studied and some correlation between measured suspension motion and road roughness measured with a high speed profilometer was found. / Dissertation (MEng (Mechanical))--University of Pretoria, 2005. / Mechanical and Aeronautical Engineering / MEng / Unrestricted

Due to the detrimental effects of ride vibrations on occupants and increasing safety concerns, improvement in vehicle dynamic characteristics has become a key focus of researchers. Typically, ride and handling problems have been dealt with independently. There is a dearth of vehicle models capable of capturing occupant biodynamics and its implication on vehicle ride and handling. Also in general, the objective of conventional control systems has been to attenuate vertical dynamic response of the sprung mass of a vehicle. Feedback control based algorithms are predominantly used in active/semi-active suspensions that ignore the biodynamics of occupants. In the current work, a new 50 degree-of-freedom (DOF) combined nonlinear multi-occupant vehicle model is developed using the lumped parameter modelling (LPM) approach. The current model provides a platform for performing a combined study of ride, handling and occupant biodynamics. The model is capable of simulating the combined effect of sitting occupancies, road inputs and driving maneuvers on biodynamic responses. It is analyzed using MATLAB/SIMULINK functionalities and validated by independently correlating the computed responses with existing experimental results. A study is performed on ride behavior of a vehicle-occupant system under two different transient road inputs. In addition, the effect of road roughness on vehicle ride is also studied. Random road profiles are generated from road roughness spectrum given in the ISO 8608:1995 manual. Insights are developed into the ride dynamics of a vehicle traversing over roads of classes A, B, C and D at given test velocities. The effect of sitting occupancies and vehicle velocities on lateral dynamics is also studied. Results underscore the need for considering sitting occupancies while analyzing vehicle dynamics and also highlight the potential of the current model. Furthermore, a Moore-Penrose Pseudoinverse based feed-forward controller is developed and implemented in an independently acting semi-active seat suspension system. Feasibility of feed-forward control in primary suspensions is also investigated. Finally, issues of stability, performance and limitation of the controller are discussed.