Suspension parameters analysis for different track conditions

Dissertação de mestrado integrado em Engenharia Mecânica (área de especialização em Sistemas Mecatrónicos)Este trabalho, aqui apresentado, tem como objetivo o estudo do comportamento do sistema de suspensão de um veículo ao atravessar estradas com obstáculos, como lombas ou buracos. Para atingir este objetivo, uma vasta revisão literária foi feita. Sendo este um tópico extenso, três tipos de revisão foram feitos. Primeiro, a um estudo global à tecnologia usava hoje em dia em pneus e nos sistemas de suspensão de veículos foi compilado. Uma breve menção à cinemática de veículos é empreendida. De seguida, a dinâmica do contacto pneu/solo é sistematicamente explanada, para compreender os diversos modelos de pneu (força) existentes. Adicionalmente, os conceitos fundamentais da análise da dinâmica multicorpo são expostos para justificar a modelação do veículo como um sistema multicorpo. Com toda a teoria apresentada, os conceitos previamente explicados são aplicados na prática para a formulação de um método que visa estimar a trajetória de um veículo atravessando uma qualquer estrada. O primeiro passo a executar é a escolha do modelo de pneu a utilizar. Percebe-se que se deve usar modelos matemáticos, culminando na escolha da Magic Formula. Os passos seguintes consistem na introdução de uma metodologia, que estima o contacto entre um pneu e o solo, para simular as dinâmicas pneu/solo de um veículo. Dois métodos diferentes são expostos: o primeiro para estradas completamente planas, sem obstáculos; o segundo, para estradas com obstáculos, como lombas ou buracos. Este modelo é posteriormente inserido num programa de análise das dinâmicas multicorpo, MUBODYNA3D, e diversas simulações são realizadas. Estas simulações começam pela definição do veículo como um sistema multicorpo, com corpos conectados por juntas cinemáticas. As primeiras simulações são realizadas numa estrada plana para validar os modelos e metodologias previamente criadas. O integrador, que integra os resultados das equações do movimento para prever a trajetória, é refinado. Finalmente, simulações com estradas com obstáculos são geradas. Por fim, os resultados dessas simulações são discutidos, percebendo-se que apresentam um valor inesperado. Ao atravessar um obstáculo, as rodas perdem o contacto com a superfície, provocando a descolagem do carro. No entanto, é concluído que a análise de sistemas multicorpo é de extrema relevância para a simulação de realidades complexas, produzindo resultados precisos.This work, hereby presented, has a primary target of studying the behaviour of a road vehicle’s suspension system, while it is traversing roads with big obstacles, such as potholes or speed bumps/humps. To accomplish this task, a broad literature review was made. Since this is an extensive topic, three types of review were made. Firstly, an overview of the state-of-the-art technology used in tires and suspension systems nowadays is compiled. A brief mention to vehicle kinematics is also made. Then, the dynamics of the contact tire/road are systematically explained, in order to understand the diverse tire force models that exist. Lastly, a rundown of the fundamental concepts of multibody dynamics analysis is exposed to substantiate the modelling of a vehicle as a multibody system later on. With the theory behind, all concepts previously abridged are put to practice, into the formulation of a method to estimate the trajectory of a vehicle crossing a certain road. The first step to execute this is to choose the tire force model to use. It is seen that, in this case, the mathematical models are the best choice, which culminates in the selection of the Magic Formula model. The following steps consist of introducing the contact estimation methodology created to simulate the tire/road dynamics of a vehicle. Two different methods are exposed: the first for fully flat roads, with no obstacles; the second, for road that possess obstacles, like bumps for example. This model is then inserted into a multibody dynamics analysis program, MUBODYNA3D, and some forward dynamic simulations are performed. These simulations start with the definition of the vehicle as a multibody system, with bodies connected by kinematic joints. The first simulations are performed in flat roads to validate the models and methodologies created. The solver, that integrates the results of the equations of motion to predict the trajectory, are then refined. Finally, simulations using roads with obstacles are conducted and the results analysed. In the end, the simulations result in some unexpected behaviour from the vehicle. While crossing an obstacle, it tends to lose contact with the surface and, thus, lift off the road, which is unrealistic. Nonetheless, it is concluded that multibody systems analysis is extremely important to simulate and analyse complex realities, with precise results

Formulation of a Path-Following Joint for Multibody System Dynamics

The development and validation of a new multibody joint that constrains a body to follow a spatial path and an orientation defined by a user is presented. The resulting joint has a single degree of freedom (DOF), and maintains equivalent kinematic behaviour when compared to higher-fidelity models. As such, it is referred to as a single-DOF equivalent kinematic (SEK) joint. The primary application of this joint is in the reduction of complex multibody systems, specifically vehicle suspensions. The first formulation of the joint is developed using the user interface of MapleSim. Starting with a planar particle joint, the theory is extended to a full 3D rigid body constraint. At each development stage, the joint is successfully validated against conventional models in both Adams and MapleSim. This formulation of the joint results in the kinematic pair being represented by a system of differential algebraic equations (DAEs) which is not the desired functionality, and so a second formulation is developed. By removing the constraint of using the MapleSim user interface, the formulation can be developed from first principles. Using the path-length as the coordinate for the joint, and the Frenet-Serret equations to compute the motion and reaction spaces, the kinematic pair can be represented by a single ordinary differential equation (ODE). The theory is implemented in the MapleSim source code using the symbolic computing language Maple. The theory of the SEK joint can be extended to create different joints. The first is the compliant SEK joint. In this version of the joint, the body is constrained to move along a spatial path using a simple linear bushing model. The compliant SEK joint is useful for modeling the suspension systems of passenger cars as bushings are used extensively in these systems to increase passenger comfort. The second extension is to add an additional DOF to the SEK joint to created the double-DOF equivalent kinematic (DEK) joint. The DEK joint is useful for modelling steered suspension systems as the steering introduces an additional DOF to the suspension. The envelope of motion for the steered wheel is a surface rather than a spatial line. Once the joints are successfully validated, three example applications of the joint are shown. In the first, rigid, compliant and steered suspension models are developed and compared against high-fidelity models in Adams/Car and MapleSim. Next, a full vehicle model is assembled using the suspension models and compared against an equivalent high-fidelity full vehicle model built in MapleSim. The comparisons show the accuracy of the SEK joint as well as the simulation speed improvements it can offer compared with conventional modelling techniques. The second example, from the domain of biomechanics, shows a knee model created using the SEK joint. Finally, a roller coaster model is created to demonstrate the flexibility of the path generation algorithm to create splines that represent complex paths

Investigation of a non-linear suspension in a quarter car model

This thesis presents the study of a quarter car model which consists of a two-degree-of-freedom (2 DOF) with a linear spring and a nonlinear spring configuration. In this thesis, the use of non-linear vibration attachments is briefly explained, and a survey of the research done in this area is also discussed. The survey will show what have been done by the researches in this new field of nonlinear attachments. Also, it will be shown that this topic was not extensively researched and is a new type of research where no sufficient experimental work has been applied. As an application, a quarter car model was chosen to be investigated. The aim of the Thesis is to validate theoretically and experimentally the use of nonlinear springs in a quarter car model. Design the new type of suspension and insert it in the experimental set up, built from the ground up in the laboratory. A novel criterion for optimal ride comfort is the root mean square of the absolute acceleration specified by British standards ISO 2631-1997. A new way to reduce vibrations is to take advantage of nonlinear components. The mathematical model of the quarter-car is derived, and the dynamics are evaluated in terms of the main mass displacement and acceleration. The simulation of the car dynamics is performed using Matlab® and Simulink®. The realization of vibration reduction through one-way irreversible nonlinear energy localization which requires no pre-tuning in a quarter car model is studied for the first time. Results show that the addition of the nonlinear stiffness decreases the vibration of the sprung mass to meet optimal ride comfort standards. As the passenger is situated above the sprung mass, any reduction in the sprung mass dynamics will directly have the same effect on the passenger of the vehicle. The future is in the use of a nonlinear suspension that could provide improvement in performance over that realized by the passive, semi active and active suspension. The use of a quarter car model is simple compared to a half car model or a full car model, furthermore in the more complex models you can study the heave and the pitch of the vehicle. For the initial study of the nonlinear spring the quarter car model was sufficient enough to study the dynamics of the vehicle. Obtaining an optimum suspension system is of great importance for automotive and vibration engineer involved in the vehicle design process. The suspension affects an automobile’s comfort, performance, and safety. In this thesis, the optimization of suspension parameters which include the spring stiffness and damper coefficient is designed to compromise between the comfort and the road handling. Using Genetic algorithm an automated optimization of suspension parameters was executed to meet performance requirements specified. Results show that by optimizing the parameters the vibration in the system decreases immensely

The Effect Of Direct Yaw Moment On Human Controlled Vehicle Systems

Advances in computing technology have had a profound impact on the design and development of modern vehicle systems. These advances have provided the basis for virtual design and testing in simulated environments, as well as the development of active control systems capable of providing improved vehicle safety, efficiency, and performance. Continued developments in hybrid powertrains and on-board computing will provide for greater amounts of control, through the integration of larger numbers of actuators and more complex control schemes. The intention of this research is to investigate the effects of advanced vehicle dynamics controls on the human operated vehicle system. Hybrid electric vehicle systems incorporating multiple electric drive motors are capable of actively distributing drive and braking torque to the individual wheels of the vehicle. The modulation of these torques can be used to optimize or alter the dynamic response of the vehicle, through the application of a direct yaw moment. A control structure capable of determining and dynamically allocating appropriate control signals for over-actuated vehicle systems is proposed. A dynamic simulation of a virtual prototype BMW 330i is utilized to evaluate the effects of active drive torque vectoring on vehicle response. The effects of the proposed system on the human operator are also evaluated, through the use of driver model in-the-loop simulations. The results presented indicate the promising potential of direct yaw moment control in modulating the response of human operated vehicle systems. The interactions between the human driver model and control systems were shown to be favourable. The scientific contributions and implications of the research are detailed, including application of closed-loop simulation to engineering education. Conclusions on the efficacy of developed models, methodologies and systems are given. Finally, recommendations on potential improvements and future research regarding vehicle modelling and motion control are provided

Kineto-Dynamic Analyses of Vehicle Suspension for Optimal Synthesis

Design and synthesis of a vehicle suspension is a complex task due to constraints imposed by multiple widely conflicting kinematic and dynamic performance measures, which are further influenced by the suspension damper nonlinearity. In addition, synthesis of suspension for hybrid vehicles may involve additional design compromises among different measures in view of the limited lateral packaging space due to larger sub-frame requirements for placing the batteries. In this dissertation research, a coupled kineto-dynamic analysis method is proposed for synthesis of vehicle suspension system, including its geometry and joint coordinates, and asymmetric damping properties. Quarter-car and two-dimensional roll plane kineto-dynamic models of linkage suspensions are proposed for coupled kinematic and dynamic analyses, and optimal suspension geometry and damper syntheses. The kinematic responses of quadra-link and double wishbone types of suspensions are evaluated using the single-wheel kinematic models. Laboratory measurements were performed and the data were applied to demonstrate validity of the 3- dimensional kinematic model. A sensitivity analysis method is proposed to study influences of various joint coordinates on kinematic responses and to identify a desirable synthesis. A kineto-dynamic quarter car model comprising linkage kinematics of a double wishbone type of suspension together with a linear, and single- and two-stage asymmetric damper is subsequently proposed for coupled kinematic and dynamic analyses. The coupling between the various kinematic and dynamic responses, and their significance are iv discussed for suspension synthesis. The effects of damping asymmetry on coupled responses are thoroughly evaluated under idealized bump/pothole and random road excitations, which revealed conflicting design requirements under different excitations. A constrained optimization problem is formulated and solved to seek design guidance for synthesis of a two-stage asymmetric damper that would yield an acceptable compromise among the kinematic and dynamic performance measures under selected excitations and range of forward speeds. The coupled kinematic and dynamic responses in the roll plane are further analyzed through development and analysis of a kineto-dynamic roll-plane vehicle model comprising double wishbone type of suspensions, asymmetric damping and an antiroll bar. The results are discussed to illustrate conflicting kinematic responses such as bump/roll camber and wheel track variations, and an optimal geometry synthesis is derived considering the conflicting kinematic measures together with the lateral space constraint. A full-vehicle model comprising double wishbone type of suspensions is also developed in the ADAMS/car platform to study influences of faults in suspension bushings and linkages on the dynamic responses. The results of the study suggest that an optimal vehicle suspension synthesis necessitates considerations of the coupled kinematic and dynamic response analyse

Methodology for Multidisciplinary Optimization of Vehicle Suspension Systems

A manual iterative process is often used in the design process of vehicle suspension systems. This thesis aim to develop a methodology for multidisciplinary optimization of vehicle suspension systems, which can be used to introduce an optimization driven process into the design process of vehicle suspension systems. A Multibody Dynamics (MBD) model of a Strut & Coil Spring suspension system will be used as a test subject. The methodology developed includes concept screening of suspension systems, multi-objective system optimization and weight reduction using structural optimization. The initial concept screening will provide guidance to selection of important design variables. Ride comfort, handling performance, and noise, vibration, and harshness (NVH) are optimized in the multi-objective system optimization, using the Multi-Objective Genetic Algorithm (MOGA) combined with a Design Space Reduction Method (DSRM).Today, experienced engineers use their prior knowledge to create an initial ”best-guess” vehicle suspension design. This design is then iteratively improved in a manual process until it satisfies the design goals. This process is time consuming and can be improved by introducing an optimization driven design process, which replaces the manual iterative work

Proceedings of the ECCOMAS Thematic Conference on Multibody Dynamics 2015

This volume contains the full papers accepted for presentation at the ECCOMAS Thematic Conference on Multibody Dynamics 2015 held in the Barcelona School of Industrial Engineering, Universitat Politècnica de Catalunya, on June 29 - July 2, 2015. The ECCOMAS Thematic Conference on Multibody Dynamics is an international meeting held once every two years in a European country. Continuing the very successful series of past conferences that have been organized in Lisbon (2003), Madrid (2005), Milan (2007), Warsaw (2009), Brussels (2011) and Zagreb (2013); this edition will once again serve as a meeting point for the international researchers, scientists and experts from academia, research laboratories and industry working in the area of multibody dynamics. Applications are related to many fields of contemporary engineering, such as vehicle and railway systems, aeronautical and space vehicles, robotic manipulators, mechatronic and autonomous systems, smart structures, biomechanical systems and nanotechnologies. The topics of the conference include, but are not restricted to: ● Formulations and Numerical Methods ● Efficient Methods and Real-Time Applications ● Flexible Multibody Dynamics ● Contact Dynamics and Constraints ● Multiphysics and Coupled Problems ● Control and Optimization ● Software Development and Computer Technology ● Aerospace and Maritime Applications ● Biomechanics ● Railroad Vehicle Dynamics ● Road Vehicle Dynamics ● Robotics ● Benchmark ProblemsPostprint (published version

Study of Vehicle Dynamics with Planar Suspension Systems (PSS)

The suspension system of a vehicle is conventionally designed such that the spring-damper element is configured in the vertical direction, and the longitudinal connection between the vehicle chassis and wheels is always very stiff compared to the vertical one. This mechanism can isolate vibrations and absorb shocks efficiently in the vertical direction but cannot attenuate the longitudinal impacts caused by road obstacles. In order to overcome such a limitation, a planar suspension system (PSS) is proposed. This novel vehicle suspension system has a longitudinal spring-damper strut between the vehicle chassis and wheel. The dynamic performance, including ride comfort, pitch dynamics, handling characteristics and total dynamic behaviour, of a mid-size passenger vehicle equipped with such planar suspension systems is thoroughly investigated and compared with those of a conventional vehicle. To facilitate this investigation, various number of vehicle models are developed considering the relative longitudinal motions of wheels with respect to the chassis. A 4-DOF quarter-car model is used to conduct a preliminary study of the ride quality, and a pitch plane half-car model is employed to investigate the pitch dynamics in both the frequency and time domain. A 5-DOF yaw plane single-track half-car model along with a pitch plane half-car model is proposed to carry out the handling performance study, and also an 18-DOF full-car model is used to perform total dynamics study. In addition to these mathematical models, virtual full-car models are constructed in Adams/car to validate the proposed mathematical models. For the sake of prediction of the tire-ground interaction force, a radial-spring tire model is modified by adding the tire damping to generate the road excitation forces due to road disturbances in the vertical and longitudinal directions. A dynamic 2D tire friction model based on the LuGre friction theory is modified to simulate the dynamic frictional interaction in the tire-ground contact pitch. The ride quality of a PSS vehicle is evaluated in accordance with the ISO 2631 and compared with that of a conventional vehicle. It is shown that the PSS system exhibits good potential to attenuate the impact and isolate the vibration due to road excitations in both the vertical and longitudinal directions, resulting in improved vehicles’ ride and comfort quality. The relatively soft longitudinal strut can absorb the longitudinal impact and, therefore, can protect the components. The investigation of handling performance including the steady-state handling characteristics, transient and frequency responses in various scenarios demonstrates that the PSS vehicle is directionally stable and generally has comparable handling behaviour to a similar conventional vehicle. The application of PSS in vehicles can enhance the understeer trend, i.e. the understeer becomes more understeer, neutral steer becomes slightly understeer, and oversteer becomes less oversteer. The total dynamic behaviour combining the bounce, pitch, roll and the longitudinal dynamics under various scenarios such as differential brake-in-turn and asymmetric obstacle traversing was thoroughly investigated. Simulation results illustrate that the PSS vehicle has a relatively small roll angle in a turning manoeuvre. In some cases such as passing road potholes, the PSS vehicle has a better directional stability

Implications of nonlinear suspension behaviour for feedforward control of road noise in cars

Active control offers a lightweight solution to the problem of low frequency structure-borne road noise in cars. Feedforward control of road noise is predominantly limited by the difficulty of finding reference signals that are highly coherent with the sound in the cabin. One factor that could restrict the coherence of the reference signals, and therefore the performance of a linear control system, is the behaviour of nonlinear components in the suspension. The purpose of this research is to identify potential sources of nonlinearity in a car’s suspension and investigate their influence on the propagation of structure-borne road noise into the cabin. The details of experiments and simulations are described that aim to quantify the role of nonlinearity in the suspension’s dynamics, and determine to what extent it limits the performance of a linear feedforward road noise control system. The results of experiments conducted on a Nissan Leaf test vehicle are presented that establish the theoretical maximum noise reduction that can be achieved with a linear control system using reference sensors placed at the wheel hubs. Laboratory experiments on the components in the Nissan Leaf’s suspension are presented that identify the hydraulic dampers as the main source of nonlinearity in the road noise transmission path. Models of the key components in a car suspension are developed based on the results of the experiments. Models for the front and rear dampers in the Nissan Leaf are validated up to 300 Hz, and analysed to reveal the mechanisms causing their nonlinear dynamics. Models for the bushings, springs and wishbone are developed and combined into a full suspension model. The suspension model’s predictions add to the evidence from the measurements that road noise transmission is strongly influenced by nonlinearity in the damper. Some implications of the suspension’s nonlinear dynamics for feedforward control of road noise are then explored. The linear control systems used currently are often limited to one reference sensor on each suspension; a simplified analysis of a two transmission path suspension system shows that, if one path is nonlinear, a linear control system with a single reference sensor can not cancel all of the noise generated at the wheel. This thesis presents strong evidence that nonlinear suspension dynamics limit the performance of feedforward road noise controllers. A nonlinear model of vibration transmission through a suspension is developed and guidelines are suggested for reference sensor selection.Bose Corporatio

Combined Time and Frequency Domain Approaches to the Operational Identification of Vehicle Suspension Systems

This research is an investigation into the identification of vehicle suspension systems from measured operational data. Methods of identifying unknown parameter values in dynamic models, from experimental data, are of considerable interest in practice. Much of the focus has been on the identification of mechanical systems when both force and response data are obtainable. In recent years a number of researchers have turned their focus to the identification of mechanical systems in the absence of a measured input force. This work presents a combined time and frequency domain approach to the identification of vehicle suspension parameters using operational measurements. An end– to–end approach is taken to the problem which involves a combination of focused experimental design, well established force–response testing methods and vehicle suspension experimental testing and simulation. A quarter car suspension test rig is designed and built to facilitate experimental suspension system testing. A novel shock absorber force measurement set–up is developed allowing the measurement of shock absorber force under both isolated and operational testing conditions. The quarter car rig is first disassembled and its major components identified in isolation using traditional force–response testing methods. This forms the basis for the development of an accurate nonlinear simulation of the quarter car test rig. A comprehensive understanding of the quarter car experimental test rig dynamics is obtained before operational identification is implemented. This provides a means of validating the suspension parameters obtained using operational testing methods. A new approach to the operational identification of suspension system parameters is developed. The approach is first developed under controlled simulated conditions before being applied to the operational identification of the quarter car experimental test rig. A combination of time and frequency domain methods are used to extract sprung mass, linear stiffness and nonlinear damping model parameters from the quarter car experimental test rig. Component parameters identified under operational conditions show excellent agreement with those identified under isolated laboratory conditions