Active independent front steering for yaw-rate control and tire work-load equalization in road vehicles

Several control strategies can be implemented in road vehicles to avoid roll over, improve ride quality or customize handling performance. Handling performance is one of the crucial areas of research from the safety point of view. Most of the control strategies depend on manipulating the motion of the tires, which are the prime source of the forces acting on the vehicle. Some of the common control strategies for handling explored in recent years include: active control of tractive and/or braking torque; and a wide variations in active steering control. For vehicle stability and handling improvement, Active Front and Rear Steering (AFS, ARS) prove to be excellent control techniques, as active torque control fails to generate required forces and moments in certain situations. In recent years, major research effort has been directed towards active steering control, where the steer angle of the wheels is actively controlled to improve handling performance at high speeds. Such controls, however, have limitations as they do not attempt to utilize tires' force generating potential. The present study proposes a new Active Independent Front Steering (AIFS) technique with independent control for each front wheel. A non-linear 4-wheel vehicle model incorporating tire 'Magic formula' and load shifts in longitudinal and lateral direction is studied. This model agrees well with a simpler bicycle model and CarSim simulation. The 4-wheel vehicle model with proposed AIFS is simulated for step and sinusoidal lane-change inputs. A simple PI control algorithm that differentiates between under and oversteer handling characteristics is developed and utilized for the simulations. The results show that by controlling one wheel only, AIFS can provide the ideal yaw-rate and trajectory responses at any speed, and the performances are as good as those obtained by AFS and significantly better than conventional uncontrolled system. Furthermore, AIFS is shown to equalize the tire workload at the left and right front tires improving the vehicle's ability to generate maximum possible lateral force. Only exception to this is when the vehicle is strongly oversteer. It is also shown that this limitation can be overcome by introducing an AIFS where both wheels are actively controlled. A physical design using tandem planetary gear trains is proposed for the AIFS that can provide the required control and is fail safe. The present is a first investigation of AIFS control that has significant potential for the integrated control of road vehicles and is identified in proposed future studies

Reconfigurable Integrated Control for Urban Vehicles with Different Types of Control Actuation

Urban vehicles are designed to deal with traffic problems, air pollution, energy consumption, and parking limitations in large cities. They are smaller and narrower than conventional vehicles, and thus more susceptible to rollover and stability issues. This thesis explores the unique dynamic behavior of narrow urban vehicles and different control actuation for vehicle stability to develop new reconfigurable and integrated control strategies for safe and reliable operations of urban vehicles. A novel reconfigurable vehicle model is introduced for the analysis and design of any urban vehicle configuration and also its stability control with any actuation arrangement. The proposed vehicle model provides modeling of four-wheeled (4W) vehicles and three- wheeled (3W) vehicles in Tadpole and Delta configurations in one set of equations. The vehicle model is also reconfigurable in the sense that different configurations of control actuation can be accommodated for controller design. To develop the reconfigurable vehicle model, two reconfiguration matrices are introduced; the corner and actuator reconfiguration matrices that are responsible for wheel and actuator configurations, respectively. Simulation results show that the proposed model properly matches the high-fidelity CarSim models for 3W and 4W vehicles. Rollover stability is particularly important for narrow urban vehicles. This thesis investigates the rollover stability of three-wheeled vehicles including the effects of road angles and road bumps. A new rollover index (RI) is introduced, which works for various road conditions including tripped and un-tripped rollovers on flat and sloped roads. The proposed RI is expressed in terms of measurable vehicle parameters and state variables. In addition to the effects of the lateral acceleration and roll angle, the proposed RI accounts for the effects of the longitudinal acceleration and the pitch angle, as well as the effects of road angles. Lateral and vertical road inputs are also considered since they can represent the effects of curbs, soft soil, and road bumps as the main causes of tripped rollovers. Sensitivity analysis is provided to evaluate and compare the effects of different vehicle parameters and state variables on rollover stability of 3W vehicles. A high-fidelity CarSim model for a 3W vehicle has been used for simulation and evaluation of the proposed RI accuracy. As a potentially useful mechanism for urban vehicles, wheel cambering is also investigated in this study to improve both lateral and rollover stability of narrow vehicles. A suspension system with active camber has an additional degree of freedom for changing the camber angle through which vehicle handling and stability can be improved. Conventionally, camber has been known for its ability to increase lateral forces. In this thesis, the benefits of cambering for rollover stability of narrow vehicles are also investigated and compared with a vehicle tilt mechanism. The simulation results indicate that active camber systems can improve vehicle lateral stability and rollover behavior. Furthermore, by utilizing more friction forces near the limits, the active camber system provides more improvement in maneuverability and lateral stability than the active front steering does. The proposed reconfigurable vehicle model leads us to the development of a general integrated reconfigurable control structure. The reconfigurable integrated controller can be used to meet different stability objectives of 4W and 3W vehicles with flexible combinations of control actuation. Employing the reconfigurable vehicle model, the proposed unified controller renders reconfigurability and can be easily adapted to Tadpole and Delta configurations of 3W as well as 4W vehicles without reformulating the problem. Different types and combinations of actuators can be selected for the control design including or combination of differential braking, torque vectoring, active front steering, active rear steering, and active camber system. The proposed structure provides integrated control of the main stability objectives including handling improvement, lateral stability, traction/braking control, and rollover prevention. The Model Predictive Control (MPC) approach is used to develop the reconfigurable controller. The performance of the introduced controller has been evaluated through CarSim simulations for different vehicles and control actuation configurations

Torque vectoring based drive assistance system for turning an electric narrow tilting vehicle

The increasing number of cars leads to traffic congestion and limits parking issue in urban area. The narrow tilting vehicles therefore can potentially become the next generation of city cars due to its narrow width. However, due to the difficulty in leaning a narrow tilting vehicle, a drive assistance strategy is required to maintain its roll stability during a turn. This article presents an effective approach using torque vectoring method to assist the rider in balancing the narrow tilting vehicles, thus reducing the counter-steering requirements. The proposed approach is designed as the combination of two torque controllers: steer angle–based torque vectoring controller and tilting compensator–based torque vectoring controller. The steer angle–based torque vectoring controller reduces the counter-steering process via adjusting the vectoring torque based on the steering angle from the rider. Meanwhile, the tilting compensator–based torque vectoring controller develops the steer angle–based torque vectoring with an additional tilting compensator to help balancing the leaning behaviour of narrow tilting vehicles. Numerical simulations with a number of case studies have been carried out to verify the performance of designed controllers. The results imply that the counter-steering process can be eliminated and the roll stability performance can be improved with the usage of the presented approach

A Real-time Nonlinear Model Predictive Controller for Yaw Motion Optimization of Distributed Drive Electric Vehicles

This paper proposes a real-time nonlinear model predictive control (NMPC) strategy for direct yaw moment control (DYC) of distributed drive electric vehicles (DDEVs). The NMPC strategy is based on a control-oriented model built by integrating a single track vehicle model with the Magic Formula (MF) tire model. To mitigate the NMPC computational cost, the continuation/generalized minimal residual (C/GMRES) algorithm is employed and modified for real-time optimization. Since the traditional C/GMRES algorithm cannot directly solve the inequality constraint problem, the external penalty method is introduced to transform inequality constraints into an equivalently unconstrained optimization problem. Based on the Pontryagin’s minimum principle (PMP), the existence and uniqueness for solution of the proposed C/GMRES algorithm are proven. Additionally, to achieve fast initialization in C/GMRES algorithm, the varying predictive duration is adopted so that the analytic expressions of optimally initial solutions in C/GMRES algorithm can be derived and gained. A Karush-Kuhn-Tucker (KKT) condition based control allocation method distributes the desired traction and yaw moment among four independent motors. Numerical simulations are carried out by combining CarSim and Matlab/Simulink to evaluate the effectiveness of the proposed strategy. Results demonstrate that the real-time NMPC strategy can achieve superior vehicle stability performance, guarantee the given safety constraints, and significantly reduce the computational efforts

Enhancement of Vehicle Safety and Improving Vehicle Yaw Behaviour Due to Offset Collisions Using Vehicle Dynamics

This study aims to optimise Vehicle Dynamic Control Systems (VDCS) in offset impact for vehicle collision mitigation. A proposed unique 3-D full-car mathematical model is developed and solved numerically to carry out this analysis. In this model, vehicle dynamics is studied together with the vehicle crash structural dynamics. Validation of the vehicle crash structure of the proposed model is achieved to ensure that the modelling of the crumple zone and the dynamic responses are reliable. It is demonstrated from the numerical simulations that the vehicle dynamic responses are captured and analysed and the influence of VDCS is determined accurately. In addition, it is shown that the mathematical model is flexible, useful and can be used in optimisation studies

Yaw Rate and Sideslip Angle Control Through Single Input Single Output Direct Yaw Moment Control

Electric vehicles with independently controlled drivetrains allow torque vectoring, which enhances active safety and handling qualities. This article proposes an approach for the concurrent control of yaw rate and sideslip angle based on a single-input single-output (SISO) yaw rate controller. With the SISO formulation, the reference yaw rate is first defined according to the vehicle handling requirements and is then corrected based on the actual sideslip angle. The sideslip angle contribution guarantees a prompt corrective action in critical situations such as incipient vehicle oversteer during limit cornering in low tire-road friction conditions. A design methodology in the frequency domain is discussed, including stability analysis based on the theory of switched linear systems. The performance of the control structure is assessed via: 1) phase-plane plots obtained with a nonlinear vehicle model; 2) simulations with an experimentally validated model, including multiple feedback control structures; and 3) experimental tests on an electric vehicle demonstrator along step steer maneuvers with purposely induced and controlled vehicle drift. Results show that the SISO controller allows constraining the sideslip angle within the predetermined thresholds and yields tire-road friction adaptation with all the considered feedback controllers

Optimal control of motorsport differentials

Modern motorsport limited slip differentials (LSD) have evolved to become highly adjustable, allowing the torque bias that they generate to be tuned in the corner entry, apex and corner exit phases of typical on-track manoeuvres. The task of finding the optimal torque bias profile under such varied vehicle conditions is complex. This paper presents a nonlinear optimal control method which is used to find the minimum time optimal torque bias profile through a lane change manoeuvre. The results are compared to traditional open and fully locked differential strategies, in addition to considering related vehicle stability and agility metrics. An investigation into how the optimal torque bias profile changes with reduced track-tyre friction is also included in the analysis. The optimal LSD profile was shown to give a performance gain over its locked differential counterpart in key areas of the manoeuvre where a quick direction change is required. The methodology proposed can be used to find both optimal passive LSD characteristics and as the basis of a semi-active LSD control algorithm

Modelling commercial vehicle handling and rolling stability

YesThis paper presents a multi-degrees-of-freedom non-linear multibody dynamic model of a three-axle heavy commercial vehicle tractor unit, comprising a subchassis, front and rear leaf spring suspensions, steering system, and ten wheels/tyres, with a semi-trailer comprising two axles and eight wheels/tyres. The investigation is mainly concerned with the rollover stability of the articulated vehicle. The models incorporate all sources of compliance, stiffness, and damping, all with non-linear characteristics, and are constructed and simulated using automatic dynamic analysis of mechanical systems formulation. A constant radius turn test and a single lane change test (according to the ISO Standard) are simulated. The constant radius turn test shows the understeer behaviour of the vehicle, and the single lane change manoeuvre was conducted to show the transient behaviour of the vehicle. Non-stable roll and yaw behaviour of the vehicle is predicted at test speeds .90 km/h. Rollover stability of the vehicle is also investigated using a constant radius turn test with increasing speed. The articulated laden vehicle model predicted increased understeer behaviour, due to higher load acting on the wheels of the middle and rear axles of the tractor and the influence of the semi-trailer, as shown by the reduced yaw rate and the steering angle variation during the constant radius turn. The rollover test predicted a critical lateral acceleration value where complete rollover occurs. Unstable behaviour of the articulated vehicle is also predicted in the single lane change manoeuvre

A state-of-the-art review on torque distribution strategies aimed at enhancing energy efficiency for fully electric vehicles with independently actuated drivetrains

© 2019, Levrotto and Bella. All rights reserved. Electric vehicles are the future of private passenger transportation. However, there are still several technological barriers that hinder the large scale adoption of electric vehicles. In particular, their limited autonomy motivates studies on methods for improving the energy efficiency of electric vehicles so as to make them more attractive to the market. This paper provides a concise review on the current state-of-the-art of torque distribution strategies aimed at enhancing energy efficiency for fully electric vehicles with independently actuated drivetrains (FEVIADs). Starting from the operating principles, which include the "control allocation" problem, the peculiarities of each proposed solution are illustrated. All the existing techniques are categorized based on a selection of parameters deemed relevant to provide a comprehensive overview and understanding of the topic. Finally, future concerns and research perspectives for FEVIAD are discussed