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

Integration of Active Systems for a Global Chassis Control Design

Vehicle chassis control active systems (braking, suspension, steering and driveline), from the first ABS/ESC control unit to the current advanced driver assistance systems (ADAS), are progressively revolutionizing the way of thinking and designing the vehicle, improving its interaction with the surrounding world (V2V and V2X) and have led to excellent results in terms of safety and performances (dynamic behavior and drivability). They are usually referred as intelligent vehicles due to a software/hardware architecture able to assist the driver for achieving specific safety margin and/or optimal vehicle dynamic behavior. Moreover, industrial and academic communities agree that these technologies will progress till the diffusion of the so called autonomous cars which are able to drive robustly in a wide range of traffic scenarios. Different autonomous vehicles are already available in Europe, Japan and United States and several solutions have been proposed for smart cities and/or small public area like university campus. In this context, the present research activity aims at improving safety, comfort and performances through the integration of global active chassis control: the purposes are to study, design and implement control strategies to support the driver for achieving one or more final target among safety, comfort and performance. Specifically, the vehicle subsystems that are involved in the present research for active systems development are the steering system, the propulsion system, the transmission and the braking system. The thesis is divided into three sections related to different applications of active systems that, starting from a robust theoretical design procedure, are strongly supported by objective experimental results obtained fromHardware In the Loop (HIL) test rigs and/or proving ground testing sessions. The first chapter is dedicated to one of the most discussed topic about autonomous driving due to its impact from the social point of view and in terms of human error mitigation when the driver is not prompt enough. In particular, it is here analyzed the automated steering control which is already implemented for automatic parking and that could represent also a key element for conventional passenger car in emergency situation where a braking intervention is not enough for avoiding an imminent collision. The activity is focused on different steering controllers design and their implementation for an autonomous vehicle; an obstacle collision avoidance adaptation is introduced for future implementations. Three different controllers, Proportional Derivative (PD), PD+Feedforward (FF) e PD+Integral Sliding Mode (ISM), are designed for tracking a reference trajectory that can be modified in real-time for obstacle avoidance purposes. Furthermore, PD+FF and PD+ISM logic are able to improve the tracking performances of automated steering during cornering maneuvers, relevant fromthe collision avoidance point of view. Path tracking control and its obstacle avoidance enhancement is also shown during experimental tests executed in a proving ground through its implementation for an autonomous vehicle demonstrator. Even if the activity is presented for an autonomous vehicle, the active control can be developed also for a conventional vehicle equipped with an Electronic Power Steering (EPS) or Steer-by-wire architectures. The second chapter describes a Torque Vectoring (TV) control strategy, applied to a Fully Electric Vehicle (FEV) with four independent electric motor (one for each wheel), that aims to optimize the lateral vehicle behavior by a proper electric motor torque regulation. A yaw rate controller is presented and designed in order to achieve a desired steady-state lateral behaviour of the car (handling task). Furthermore, a sideslip angle controller is also integrated to preserve vehicle stability during emergency situations (safety task). LQR, LQR+FF and ISM strategies are formulated and explained for yaw rate and concurrent yaw rate/sideslip angle control techniques also comparing their advantages and weakness points. The TV strategy is implemented and calibrated on a FEV demonstrator by executing experimental maneuvers (step steer, skid pad, lane change and sequence of step steers) thus proving the efficacy of the proposed controller and the safety contribution guaranteed by the sideslip control. The TV could be also applied for internal combustion engine driven vehicles by installing specific torque vectoring differentials, able to distribute the torque generated by the engine to each wheel independently. The TV strategy evaluated in the second chapter can be influenced by the presence of a transmission between themotor (or the engine) and wheels (where the torque control is supposed to be designed): in addition to the mechanical delay introduced by transmission components, the presence of gears backlashes can provoke undesired noises and vibrations in presence of torque sign inversion. The last chapter is thus related to a new method for noises and vibration attenuation for a Dual Clutch Transmission (DCT). This is achieved in a new way by integrating the powertrain control with the braking system control, which are historically and conventionally analyzed and designed separately. It is showed that a torsional preload effect can be obtained on transmission components by increasing the wheel torque and concurrently applying a braking wheel torque. For this reason, a pressure following controller is presented and validated through a Hardware In the Loop (HIL) test rig in order to track a reference value of braking torque thus ensuring the desired preload effect and noises reduction. Experimental results demonstrates the efficacy of the controller, also opening new scenario for global chassis control design. Finally, some general conclusions are drawn and possible future activities and recommendations are proposed for further investigations or improvements with respect to the results shown in the present work

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

Efficient simulation of non-linear kerb impact events in ground vehicle suspensions

In the increasing competition which pervades the automobile sector, it is necessary to develop simple methods to enable prediction of suspension loading level envelope in an early development stage. For this purpose, the FORD specified standard driving manoeuvres, based on kerb strike and pothole braking, inducing worst case loading scenarios are employed. The damaging nature of these tests and the relatively expensive physical prototypes make simple simulation models essential. These models should cope with an initial rudimentary assessment, but must suffice to predict the maximum wheel centre loads with a reasonable degree of accuracy. Enhanced model features are required to represent edge-type tyre deformation and impulsive bumper deflection. State of the art approaches are physical tyre models extended to rim clash modelling and rheological bumper models embedded in an multibody system (MBS) environment. These enhancements lead to increased complexity. The thesis proposes a minimal parameter vehicle model, tailored to predict vertical suspension loads caused by the FORD kerb strike manoeuvre. Since the focus is put on model simplicity, an in-plane bicycle model is extended to 7 degrees of freedom. Nonlinear and hysteretic characteristics of the bump-stop elements are included through use of a spatial map concept, based on displacement and velocity dependent hysteresis. Furthermore, a static tyre model is described to predict the radial stiffness against penetration of an edge and flat-type rigid body geometry. The full mathematical model is derived on the basis of the shell theory and represented in terms of few geometrical input parameters. A distinct tyre model, representing the tyre belt as a multi-link chain is also derived to confirm the assumptions made in the simple mathematical model. Model validation is supported through experiments at both component and system levels. It is shown that the bumper map concept provides an accurate, yet simple alternative to a rheological model, if applied to polyurethane foam type bumpers. This approach is also confirmed for the tyre model, substituting a comprehensive physical model approach

On the model-based design of front-to-total anti-roll moment distribution controllers for yaw rate tracking

In passenger cars active suspensions have been traditionally used to enhance comfort through body control, and handling through the reduction of the tyre load variations induced by road irregularities. However, active suspensions can also be designed to track a desired yaw rate profile through the control of the anti-roll moment distribution between the front and rear axles. The effect of the anti-roll moment distribution relates to the nonlinearity of tyre behaviour, which is difficult to capture in the linearised vehicle models normally used for control design. Hence, the tuning of anti-roll moment distribution controllers is usually based on heuristics. This paper includes an analysis of the effect of the lateral load transfer on the lateral axle force and cornering stiffness. A linearised axle force formulation is presented, and compared with a formulation from the literature, based on a quadratic relationship between cornering stiffness and load transfer. Multiple linearised vehicle models for control design are assessed in the frequency domain, and the respective controllers are tuned through optimisation routines. Simulation results from a nonlinear vehicle model are discussed to analyse the performance of the controllers, and show the importance of employing accurate models of the lateral load transfer effect during control design

Complexity reduction in automotive design and development

Thesis (S.M.)--Massachusetts Institute of Technology, System Design & Management Program, 2005.Includes bibliographical references (p. 117-118).Automobiles are complex products. High product complexity drives high levels of design and process complexity and complicatedness. This thesis attempts to reduce complicatedness in the automotive vehicle design and development process utilizing systems engineering tools including the design structure matrix (DSM) and axiomatic design concepts. The title of the thesis is a misnomer; complexity in automotive design and development is not "going away", but through the use of system engineering tools it is believed that the complicatedness of automotive design can be reduced and the consequences of decisions can be better understood at earlier stages in product development. A holistic view of the complexity and complicatedness challenge is considered, in order to identify high leverage points and generic insights that can be carried forward to future product development efforts. The goal is to translate generalized learning and systems thinking to the application of systems tools and processes that enable an understanding of complexity, in order to design better operating policies that guide positive change in systems. The analysis starts with considerations across the automotive enterprise, then the focus sharpens to the early stages of the product development process. Then a more detailed level of abstraction is considered when the automotive chassis tuning process and the interactions between the vehicle dynamics and noise and vibration (NVH) attributes are considered. The automotive rear suspension design is used to illustrate the concepts at the detailed level of abstraction. A rear suspension system case study is included, as it met a number of the challenges inherent in large-scale systems; it provides the elements of a technical challenge(cont.) and the integration of business and engineering issues, while encompassing detailed and broad issues that across different parts of the organization. The analysis demonstrates that the complicatedness of systems can be reduced and complexity can be managed through the use of the design structure matrix and axiomatic design concepts. Recommendations are made to foster improved decision-making that will result in improved automobiles and include the following: start simply with the application of these concepts on the critical few interactions that drive system performance, manage information explicitly, account and provision for risks in the development process, and reduce complexity and complicatedness through reuse.by Ronald J. Ziegler.S.M

Objective Tyre Development : Definition and Analysis of Tyre Characteristics and Quantification of their Conflicts

The present work focuses on tyres for passenger cars, especially on its influence on power loss, lateral dynamics, ride comfort and interior noise. The objective of the work is the quantification of conflicts between four selected requirements considering the physical constraints given by the tyre. The method proposed in the present book is based on a set of functional tyre characteristics, a physical tyre model and a procedure for identifying and quantifying the conflicts

AN INTEGRATED SYSTEMS ENGINEERING METHODOLOGY FOR DESIGN OF VEHICLE HANDLING DYNAMICS

The primary objective of this research is to develop an integrated system engineering methodology for the conceptual design of vehicle handling dynamics early on in the product development process. A systems engineering-based simulation framework is developed that connects subjective, customer-relevant handling expectations and manufacturers\u27 brand attributes to higher-level objective vehicle engineering targets and consequently breaks these targets down into subsystem-level requirements and component-level design specifications. Such an integrated systems engineering approach will guide the engineering development process and provide insight into the compromises involved in the vehicle-handling layout, ultimately saving product development time and costs and helping to achieve a higher level of product maturity early on in the design phase. The proposed simulation-based design methodology for the conceptual design of vehicle handling characteristics is implemented using decomposition-based Analytical Target Cascading (ATC) techniques and evolutionary, multi-objective optimization algorithms coupled within the systems engineering framework. The framework is utilized in a two-layer optimization schedule. The first layer is used to derive subsystem-level requirements from overall vehicle-level targets. These subsystem-level requirements are passed on as targets to the second layer of optimization, and the second layer derives component-level specifications from the subsystem-level requirements obtained from the first step. The second layer optimization utilizes component-level design variables and analysis models to minimize the difference between the targets transferred from the vehicle level and responses generated from the component-level analysis. An iterative loop is set up with an objective to minimize the target/response consistency constraints (i.e., the targets at the vehicle level are constantly rebalanced to achieve a consistent and feasible solution). Genetic Algorithms (GAs) are used at each layer of the framework. This work has contributed towards development of a unique approach to integrate market research into the vehicle handling design process. The framework developed for this dissertation uses Original Equipment Manufacturer\u27s (OEM\u27s) brand essence information derived from market research for the derivation and balancing of vehicle-level targets, and guides the chassis design direction using relative brand attribute weights. Other contributions from this research include development of empirical relationships between key customer-relevant vehicle handling attributes selected from market survey and the various scenarios and objective metrics of vehicle handling, development of a goal programming based approach for the selection of the best solution from a set of Pareto-optimal solutions obtained from genetic algorithms and development of Vehicle Handling Bandwidth Diagrams