On the Benefits of Using Object-Oriented Programming for the Objective Evaluation of Vehicle Dynamic Performance in Concurrent Simulations

Assessing passenger cars’ dynamic performance is a critical aspect for car industries, due to its impact on the overall vehicle safety evaluation and the subjective nature of the involved handling and comfort metrics. Accordingly, ISO standards, such as ISO 4138 and ISO 3888, define several specific driving tests to assess vehicle dynamics performance objectively. Consequently, proper evaluation of the dynamic behaviour requires measuring several physical quantities, including accelerations, speed, and linear and angular displacements obtained after instrumenting a vehicle with multiple sensors. This experimental activity is highly demanding in terms of hardware costs, and it is also significantly time-consuming. Several approaches can be considered for reducing vehicle development time. In particular, simulation software can be exploited to predict the approximate behaviour of a vehicle using virtual scenarios. Moreover, motion platforms and detail-scalable numerical vehicle models are widely implemented for the purpose. This paper focuses on a customized simulation environment developed in C++, which exploits the advantages of object-oriented programming. The presented framework strives to perform concurrent simulations of vehicles with different characteristics such as mass, tyres, engine, suspension, and transmission systems. Within the proposed simulation framework, we adopted a hierarchical and modular representation. Vehicles are modelled by a 14 degree-of-freedom (DOF) full-vehicle model, capable of capturing the dynamics and complemented by a set of scalable-detail models for the remaining sub-systems such as tyre, engine, and steering system. Furthermore, this paper proposes the usage of autonomous virtual drivers for a more objective evaluation of vehicle dynamic performances. Moreover, to further evaluate our simulator architecture’s efficiency and assess the achieved level of concurrency, we designed a benchmark able to analyse the scaling of the performances with respect to the number of different vehicles during the same simulation. Finally, the paper reports the proposed simulation environment’s scalability resulting from a set of different and varying driving scenarios

Integrated vehicle dynamics control using active steering, driveline and braking

This thesis investigates the principle of integrated vehicle dynamics control through proposing a new control configuration to coordinate active steering subsystems and dynamic stability control (DSC) subsystems. The active steering subsystems include Active Front Steering (AFS) and Active Rear Steering (ARS); the dynamic stability control subsystems include driveline based, brake based and driveline plus brake based DSC subsystems. A nonlinear vehicle handling model is developed for this study, incorporating the load transfer effects and nonlinear tyre characteristics. This model consists of 8 degrees of freedom that include longitudinal, lateral and yaw motions of the vehicle and body roll motion relative to the chassis about the roll axis as well as the rotational dynamics of four wheels. The lateral vehicle dynamics are analysed for the entire handling region and two distinct control objectives are defined, i.e. steerability and stability which correspond to yaw rate tracking and sideslip motion bounding, respectively. Active steering subsystem controllers and dynamic stability subsystem controller are designed by using the Sliding Mode Control (SMC) technique and phase-plane method, respectively. The former is used as the steerability controller to track the reference yaw rate and the latter serves as the stability controller to bound the sideslip motion of the vehicle. Both stand-alone controllers are evaluated over a range of different handling regimes. The stand-alone steerability controllers are found to be very effective in improving vehicle steering response up to the handling limit and the stand-alone stability controller is found to be capable of performing the task of maintaining vehicle stability at the operating points where the active steering subsystems cannot. Based on the two independently developed stand-alone controllers, a novel rule based integration scheme for AFS and driveline plus brake based DSC is proposed to optimise the overall vehicle performance by minimising interactions between the two subsystems and extending functionalities of individual subsystems. The proposed integrated control system is assessed by comparing it to corresponding combined control. Through the simulation work conducted under critical driving conditions, the proposed integrated control system is found to lead to a trade-off between stability and limit steerability, improved vehicle stability and reduced influence on the longitudinal vehicle dynamics

Development of an Electronic Stability Control for Improved Vehicle Handling using Co-Simulation

The research project focuses on integrating the algorithms of recent automotive Electronic Stability Control (ESC) technologies into a commercial multi-body dynamics (MBD) software for full vehicle simulations. Among various control strategies for ESC, the sliding mode control (SMC) method is proposed to develop these algorithms, as it is proven to be excellent at overcoming the effect of uncertainties and disturbances. The ESC model integrates active front steering (AFS) system and direct yaw moment control (DYC) system, using differential braking system, therefore the type of the ESC model is called as integrated vehicle dynamic control (IVDC) system. The IVDC virtual model will be designed using a specialized control system software, called Simulink. The controller model will be used to perform full vehicle simulations, such as sine with dwell (SwD) and double lane change (DLC) tests on Simulink to observe its functionality in stabilizing vehicles. The virtual nonlinear full vehicle model in CarSim will be equipped with the IVDC virtual model to ensure that the proposed IVDC virtual model passes the regulations that describes the ESC homologation process for North America and European countries, each defined by National Highway Traffic Safety Administration (NHTSA) and United Nations (UN). The proposed research project will enable automotive engineers and researchers to perform full vehicle virtual simulations with ESC capabilities

Mild Hybrid Electric Vehicles: Powertrain Optimization for Energy Consumption, Driveability and Vehicle Dynamics Enhancements

This thesis deals with the modeling, the design and the control of mild hybrid electric vehicles. The main goal is to develop accurate design tools and methodologies for preliminary system and component level analysis. Particular attention is devoted to the configuration in which an electric machine is mounted on the rear axle of a passenger car. The use of such a machine in parallel with the internal combustion engine allows one to exploit different functionalities that are able to reduce the overall fuel consumption of the vehicle. In addition, the indirect coupling between the thermal and the electric machine, realized through the road and not by means of mechanical couplers, together with the position of the latter in the overall vehicle chassis system, enables such an architecture to be efficient both from the energy recovery and the full electric driving point of view. Chapter 1 introduces the problem of fuel consumption and emissions reduction in the overall world context and presents the main hybrid architectures available. Chapter 2 is devoted to the study of the influence of the electric machine position in the powertrain regarding the regenerative braking potentialities concerned. The model considered for the analysis will be described on each of its subcomponents. The braking performance of the vehicle in electric mode is presented considering no losses in the electric powertrain (electric motor, battery, inverter). Chapter 3 is dedicated to the design of an electric machine for a rear axle powertrain. The specifications of such machine are optimized considering both the vehicle and the application under analysis. The design takes into account analytical techniques for the computation of electrical parameters (such as phase and DC currents) and the torque - speed map, as well as numerical ones for its thermal behavior. In Chapter 4 the electrical and thermal characteristics of the designed electric motor are implemented in the model presented in Chapter 2. The overall vehicle model is therefore used both to assess a simple torque split strategy between thermal and electric machine and to perform an optimal sizing of the battery considering all the limitations imposed by the electric powertrain (e. g. maximum currents, maximum temperatures). Chapter 5 makes a step forward and analyzes the different implications that the use of the rear axle electric motor to brake the vehicle has on the vehicle dynamics. Open loop analysis will present a degradation of the vehicle handling comfort caused by the introduction of an oversteering moment to the vehicle. Through the use of a simplified vehicle model, the introduced oversteering yaw moment is evaluated, while a control strategy based on a new stability detector will show how to find a trade off between handling comfort and regenerable energy. At last, Chapter 6 deals with the problem of longitudinal driving comfort. Drivelines and chassis are lightly damped systems and the application of an impulsive torque imposed by the driver can cause the vehicle longitudinal acceleration (directly perceived by the driver) to be oscillating and non smooth. A sensitivity analysis on a conventional powertrain is presented demonstrating which of the different components are more influential in the different modes of vibration, and possible solutions to improve the driveability are proposed. One of these relates to the use of the rear axle electric machine in order to give more responsiveness to the vehicle. Finally, concluding remarks are given in Chapter 7

Integrated Stability and Tracking Control System for Autonomous Vehicle-Trailer Systems

The addition of a trailer to a vehicle significantly changes the dynamics of a single-vehicle and generates new instability modes including jackknifing and snaking. Understanding of the dynamics of these modes leads to the development of more effective control strategies for improved stability and handling. In addition, vehicle-trailer systems suffer from the off-tracking problem meaning that the path of the trailer rear end differs from that of the vehicle front end. Off-tracking makes these vehicles less maneuverable and increases swept path of the vehicle, especially in urban areas and tight spaces. Vehicle active safety systems have been extensively developed over the past decades to improve vehicle handling and assist the driver to keep the vehicle under control in unfavorable driving situations. Such active safety systems, however, are not well developed for vehicle-trailer systems specialty to control the above-mentioned instability modes. In addition to the above active safety systems, off-tracking of vehicle-trailers is another aspect that is essential in path planning and path tracking of autonomous vehicle-trailers. In this thesis, first, phase portraits are used to study the non-linear dynamics of the system through state trajectories and equilibrium point locations of a vehicle-trailer system, with respect to the inputs and also the loading conditions of the trailer. By the study of the phase portraits, the foundation of the vehicle-trailer yaw instability is recognized and a two-dimensional stable region as the stability envelope is defined. This stability envelope is utilized to prevent unnecessary control interventions while the vehicle is operating in the safe stability region whereas the controller is allowed to effectively interfere when the vehicle crosses the stability envelope. To handle multiple control actions in the vehicle and trailer units, a control structure with two hierarchical layers is proposed. In the upper layer, a model predictive controller is formulated as a quadratic optimization problem with a virtual control action for each degree of freedom of the vehicle dynamic model. In this formulation, the developed stability envelope is constructed as state constraints along with control action constraints. In the lower layer, a control allocation approach optimally transforms the virtual control actions provided by the upper layer into steering and/or braking commands for each wheel. In this approach, actuator failure in addition to actuator and tire capacity constraints is taken into account in real-time. A hybrid A*-based motion planning is developed to generate a trajectory while considering the trailer effect in terms of stability in high speed and off-tracking in high curvature paths. The proposed motion planning utilizes a hybrid A* algorithm combined with potential fields to find a feasible and collision-free trajectory for the vehicle-trailer system. To assess the performance of the proposed control structure in instability prevention both in snaking and jackknifing, different simulations are conducted using different control actions. Additionally, the fault tolerance and robustness of the proposed controller are investigated. To validate the real-time performance of the proposed control strategy, experimental tests are performed on a vehicle-trailer system with differential braking capability. The results show that the proposed control strategy is able to effectively prevent both instability modes as well as unnecessary engagement of the control action to reduce control intervention. The performance of the developed motion planning module is also evaluated for normal driving, obstacle avoidance, off-tracking compensation, and crash mitigation using high-fidility Carsim model. It is observed that proposed motion planning is able to effectively satisfy all the expected requirements

Vehicle handling control using active differentials

This thesis describes an investigation into vehicle handling control using active differentials in the rear axle of a motor vehicle. Such devices are able to transfer torque between the rear wheels and have traditionally been used to improve traction whilst minimising the impact on vehicle handling. However, the capacity to generate a lateral torque difference across an axle also gives them the potential to be used for yaw moment control. In order to generate a rigorous assessment of this potential, the investigation is carried out in three distinct phases. Firstly, an analysis of the scope for modifying vehicle handling given unrestricted control over torque transfer between the rear wheels is carded out in the simulation environment. For this purpose an idealised yaw sideslip controller is developed. This is used to show that an ideal active differential can have significant yaw moment authority in terms of generating both understeer and oversteer and that this can be used to actively modify a vehicle's handling balance and apply stability control at the limits of adhesion. In the second phase, the capabilities of two types of contemporary active differential, the torque vectoring differential (TVD) and active limited slip differential (ALSID), are then assessed against the ideal differential and against a brake based yaw moment controller. TVDs are found to be able to offer very similar performance to both their ideal counterpart and to the brake based system. They Gan also deliver this performance with a fraction of the energy loss that is observed in the brakes, thus making TVDs a viable proposition for applying continuous yaw control below the limits of adhesion. ALSDs, on the other hand do not offer equivalent functionality to an ideal active differential but are still shown to be very effective stability control devices. In the third phase, the ALSID results are validated on a prototype vehicle where it is shown that they do indeed offer substantial stability improvements both on high and low-P surfaces. However in order to deliver such benefits and be practical for implementation, it is also shown that significant redevelopment of the idealised controller is required. Finally, with the ALSID operating alongside a commercial brake based stability control system, it is proven that substantial reductions in brake intervention can be achieved without significant controller integration.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress

Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018

U.S. GAAP financial statements: 67th annual survey 2013 edition

https://egrove.olemiss.edu/aicpa_att/1093/thumbnail.jp