An Intelligent Predictive Algorithm for the Anti-Rollover Prevention of Heavy Vehicles for Off-Road Applications

Rollover detection and prevention are among the most critical aspects affecting the stability and safety assessment of heavy vehicles, especially for off-road driving applications. This topic has been studied in the past and analyzed in depth in terms of vehicle modelling and control algorithms design able to prevent the rollover risk. However, it still represents a serious problem for automotive carmakers due to the huge counts among the main causes for traffic accidents. The risk also becomes more challenging to predict for off-road heavy vehicles, for which the incipient rollover might be triggered by external factors, i.e., road irregularities, bank angles as well as by aggressive input from the driver. The recent advances in road profile measurement and estimation systems make road-preview-based algorithms a viable solution for the rollover detection. This paper describes a model-based formulation to analytically evaluate the load transfer dynamics and its variation due to the presence of road perturbations, i.e., road bank angle and irregularities. An algorithm to detect and predict the rollover risk for heavy vehicles is also presented, even in presence of irregular road profiles, with the calculation of the ISO-LTR Predictive Time through the Phase-Plane analysis. Furthermore, the artificial intelligence techniques, based on the recurrent neural network approach, is also presented as a preliminary solution for a realistic implementation of the methodology. The paper finally assess the efficacy of the proposed rollover predictive algorithm by providing numerical results from the simulation of the most severe maneuvers in realistic off-road driving scenarios, also demonstrating its promising predictive capabilities

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

Vehicle Dynamics Control for Rollover Mitigation

Characterized by a high ratio between the height of center of gravity and the track-width, commercial vehicle dynamics differ from passenger car dynamics. The roll stability limit, measured in terms of lateral acceleration, is much lower, while longitudinal and lateral load transfer during braking and cornering reduce the yaw stability, resulting in roll motion. Rollovers are dangerous and possible lethal accidents. This master's thesis proposes how to detect and prevent untripped rollovers on commercial vans. Two methods to predict and detect rollover are examined. An analytical one, which uses the spring deflection sensors to measure the load distribution and therefore detects wheel liftoff as an indication of possible rollover. The other one, which is used in the developed controller, considers the potential and kinetic roll energy of the vehicle. A new control system is introduced to stabilize the roll and slip dynamics of the vehicle. It is based on an energy-related Lyapunov function, which controls the yaw rate to accomplish the objectives. The controller outputs the desired braking forces on each wheel that will stabilize the vehicle. Finally, differential braking is used to take out energy from the system. Simulations of extreme maneuvers show that the control system prevents the vehicle from rollover and skidding. They also indicate that the controller is robust against uncertainties in the load conditions. Comparisons with an existing LQ-controller confirm further the promising results of the Lyapunov controller

Estimation of LTR rollover index for a high-sided tractor semitrailer vehicle under extreme crosswind conditions through dynamic simulation

Lateral load transfer ratio (LTR) is a criterion that is often used for designing ground vehicle rollover warning technologies to indicate the vehicles rollover status. Generally, LTR index depends on road geometry and vehicle characteristics. However, crosswind loads have the potential to influence the roll stability and therefore the safety of road vehicles particularly large commercial units. This study provides improved methodology for the computation of the LTR index for a high-sided tractor semitrailer vehicle under crosswind conditions. For this purpose, since experiments on real vehicles for active safety technology are difficult to carry out, a coupled simulation of transient crosswind aerodynamics and multi-body vehicle dynamics has been proposed. Based on CFD method, a large-eddy simulation (LES) technique was employed to predict the transient crosswind aerodynamic forces. Then, the predicted aerodynamic forces were input into multi-body dynamic simulations of the tractor semi-trailer vehicle that were performed through ADAMS/Car software. Simulation results show that comparing to the traditional LTR index, the LTR under crosswind is more efficient to detect manoeuvre-induced rollovers. This trailer rollover indicator that has been improved by the proposed methodology can provide more reliable information to the warning or control system in the presence of wind conditions

Narrow Urban Vehicles with an Integrated Suspension Tilting System: Design, Modeling, and Control

Narrow urban vehicles are proposed to alleviate urban transportation challenges like congestion, parking, fuel consumption, and pollution. They are designed to seat one or two people in tandem, which saves space in road infrastructures as well as improves the fuel efficiency. However, to overcome the high rollover tendency which comes as a consequence of reduced track-width ratio, tilting systems for vehicle roll motion control are suggested. Existing tilting solutions, which mechanically connect the wheel modules on both sides for motion synchronization, are not space-friendly for the narrow vehicle footprint. The mechanical linkages also add extra weight to those urban vehicles initially designed to be light-weighted. A novel integrated suspension tilting system (ISTS) is proposed in this thesis, which replaces rigid mechanical linkages with flexible hydraulic pipes and cylinders. In addition, combining the suspension and tilting into an integrated system will result in even more compact, light-weighted, and spacious urban vehicles. The concept is examined, and the suspension mechanism for the tilting application is proposed after examining various mechanisms for their complexity and space requirements. Kinematic and dynamic properties of the tilting vehicle under large suspension strokes are analyzed to optimize the mechanism design. Control of the active tilting systems for vehicle roll stability improvement is then discussed. Rather than tilting the vehicle to entirely eliminate the lateral load transfer during cornering, an integrated envelope approach considering both lateral and roll motion is proposed to improve the energy efficiency while maintaining the vehicle stability. A re-configurable integrated control structure is also developed for various vehicle configurations as well as enhancing the system robustness against actuator failures. The model predictive control (MPC) scheme is adopted considering the non-minimum phase nature of active tilting systems. The predictive feature along with the proposed roll envelope formulation provides a framework to balance the transient and steady-state performances using the tilting actuators. The suggested controller is firstly demonstrated on a vehicle roll model, and then applied to high-fidelity full vehicle models in CarSim including a four-wheeled SUV as well as a three-wheeled narrow urban vehicle. The SUV simulation results indicate the potential of using the developed envelope controller on conventional vehicles with active suspensions, while the narrow urban vehicle simulations demonstrate the feasibility of using the suggested ISTS on narrow tilting vehicles. By adopting the integrated envelope control approach, actuation effort is reduced and the vehicle handling, along with the stability in both lateral and roll, can be further improved

Untripped manoeuvre induced rollover prevention for sport utility vehicles

Rollover accidents account for a high number of serious injuries and fatalities and thus it is greatly important to reduce the number of occurrences. Although a large number of rollovers result from factors external to the vehicle design such as environmental obstacles there is a significant portion of rollover accidents which are preventable. On-road untripped rollovers are directly related to the vehicle design. It is possible to do work in this area to improve vehicle-related safety factors. During rollover, lateral acceleration acts on the centre of gravity of the vehicle over turning it about the outer wheels. Thus the method to reduce or prevent rollover of this study stemmed from decreasing the overturning moment by reducing the movement arm though which the lateral acceleration acts. This is achieved by lower the ride height of the test vehicle using slow active suspension control of the test vehicle (Land Rover Defender 110) fitted with a hydro-pneumatic suspension system. An experimental validated mathematical model representing the test vehicle is created to develop a rollover prevention control system that reduces the vehicle’s ride height and reduces the propensity to rollover. The control system applies one of three discrete suspension settings depending on the severity of the manoeuvre as well as lowering the ride height. The model is used to simulate the Fishhook 1B and the ISO 3888 Double Lane Change manoeuvres to evaluate the roll prevention system. The rollover prevention control system improved the two wheel lift off speed of the vehicle through a Fishhook 1 B manoeuvre by 64%, the body roll angle of the vehicle through the Double Lane Change manoeuvre by 13% and the body roll rate by 25.7%. The control system significantly improved the vehicle’s response with regard to smooth flat on-road untripped rollover. Further improvements are possible with the use of the proposed control system in conjunction with a fully active suspension system to allow for faster corrective action.Oorrol ongelukke is verantwoordelik vir ‘n hoe aantal van ernstige beseerings en dodelike ongelukke en dus is dit van groot belang om die hoeveelheid ongelukke te verminder. Alhoewel meeste oorrol ongelukke is as gevolg van faktore anders as die voortuig se ontwerp, soos byvoorbeeld omgewingshindernisse, is daar ‘n groot percentasie van oorrol ongelukke wat vermybaar is. On-pad onbelemmerde rollovers is direk verwant aan die voertuigontwerp. Dit is moontlik om werk in hierdie area te doen om voertuigverwante veiligheidsfaktore te verbeter. Tydens rolloverwerking tree laterale versnelling op die swaartepunt van die voertuig oor en draai dit om die buitenste wiele. Dus die metodiek in hierdie studie om oorrol te verminder of te verhoed, stem uit vermindering van die omkeer oomblik afgeneem, deur om die bewegingsarm waardeur die laterale versnelling werk, te verminder. Dit word behaal deur die rithoogte van die toetsvoertuig te verlaag deur gebruik te maak van 'n stadig aktiewe opskortingsbeheer van die toetsvoertuig (Land Rover Defender 110) wat met 'n hidro-pneumatiese suspensie stelsel toegerus is. 'N eksperimentele gevalideerde wiskundige model wat die toetsvoertuig verteenwoordig, word geskep om 'n rollover-voorkomingsbeheerstelsel te ontwikkel wat die voertuig se rithoogte verminder en die geneigdheid om oor te skakel, verminder. Die beheerstelsel pas een van drie diskrete skorsingsinstellings toe, afhangende van die erns van die maneuver asook die verlaging van die rithoogte. Die model word gebruik om die Fishhook 1B en die ISO 3888 Double Lane Change maneuvers te simuleer om die rolvoorkomingsisteem te evalueer. Die rollover-voorkomings-beheerstelsel het die twee-wiel oplig-snelheid van die voertuig verbeter deur 'n Fishhook 1 B-maneuver met 64%, die liggaamsrolhoek van die voertuig deur die Double Lane Change-maneuver met 13% en die liggaamsrolkoers met 25.7% te verbeter. Die beheersingsstelsel het die voertuig se reaksie aansienlik verbeter met betrekking tot gladde plat op-pad onbelemmerde oorrol. Verdere verbeterings is moontlik met die gebruik van die voorgestelde kontrolesisteem in samewerking met 'n ten volle aktiewe suspensie om vinniger regstellende aksie toe te laat.Dissertation (MEng)--University of Pretoria, 2018.Mechanical and Aeronautical EngineeringMEngUnrestricte

Investigations on the Roll Stability of a Semitrailer Vehicle Subjected to Gusty Crosswind Aerodynamic Forces

Threats of high crosswind gusts on running safety of modern road and rail vehicles have been reported around the world. Under high transient crosswind conditions, sudden changes in vehicle aerodynamic forces can lead to adverse effects on vehicle dynamics and stability. Moreover, due to increase in maximum speed limits and body dimensions of commercial vehicles as well as reduction in their weights, large class vehicles, in particular, are more prone to rollover accidents in strong crosswind situations, especially at cruising speeds or at exposed sites. Such crosswind accidents have been observed even at low vehicle speed of 15 m/s in adverse windy weather. It is therefore essential to conduct detailed investigations on the aerodynamic performance of commercial vehicles under crosswind conditions in order to improve their crosswind stability. In this study, estimation of unsteady aerodynamic forces acting on a high-sided tractor-trailer vehicle have been carried out based on experiential and numerical simulations. Although natural crosswind gusts are high-turbulent phenomena, and have a large variability in types and origins, this study suggests employing two gust scenarios based on two different methods: 1. Transient wind gust scenario developed in wind-tunnel to represents a high-sided tractor semitrailer vehicle moving on a road in moderate wind condition and immediately being hit by wind gust. 2. Deterministic crosswind scenario with gusts in exponential shapes has been considered to predict crosswind aerodynamic forces of a high-sided tractor semitrailer vehicle moving through wind exposed area. This scenario is specified in the Technical Specification for Interoperability (TSI) standard, but it has been employed in this study in combination with Computational Fluid Dynamics (CFD). A series of time-dependent crosswind aerodynamic forces acting on the tractor-semitrailer vehicle have been predicted. Moreover, to illustrate the potential influence of crosswind gusts on a high-sided tractor semitrailer vehicle, instantaneous gust flow structures for proposed wind scenarios and wind pressure fields were presented. The results show that both wind gust scenarios have significant unsteady effects on the side aerodynamic force and the roll moment of the vehicle. Furthermore, there are significant variations in aerodynamic loads, and the flow field becomes more complicated, consistent with the gust’s strength. These conclusions strongly suggested the importance of considering the unsteady aerodynamic forces in the analysis of heavy vehicle roll dynamics. Lateral load transfer ratio (LTR) is a criterion that is often used for designing ground vehicle rollover warning technologies to indicate the vehicles rollover status. Generally, LTR index depends on road geometry and vehicle dynamic characteristics. However, as mentioned above, crosswind loads have the potential to influence the roll stability and therefore the safety of large commercial vehicles. Therefore, this thesis presents the research carried out to improve the traditional LTR for a high-sided tractor semitrailer vehicle to be more efficient in crosswind environment. For this purpose, since experimental investigations on vehicle rollover dynamics are difficult to carry out, a coupled simulation of crosswind aerodynamic forces and multi-body vehicle dynamics has been proposed. In this method, the predicted aerodynamic forces result due to the proposed wind scenarios were input into multi-body dynamic simulations of the tractor semi-trailer vehicle that were performed through Adams/Car software. Based on this coupled analysis, dynamic responses of the vehicle to fluctuating crosswind conditions have been predicted. Moreover, all parameters of the LTR index such as body roll angle and lateral acceleration were estimated through a critical turning manoeuvre with crosswind actions. The investigation results show that, in the same manoeuvre, in comparison with the traditional LTR index (i.e., in which crosswind aerodynamic forces are ignored), the improved LTR rollover (crosswind) indicator, has successfully detected wheel lift–up conditions when crosswind aerodynamic loads are considered. Also, average values of the LTR measured under crosswind effects are about 22% higher than those of corresponding traditional LTR index. Therefore, the rollover indicator that has been improved by the proposed methodology can provide more reliable information to the warning or control system in the presence of wind conditions

Multi-Actuated Vehicle Control and Path Planning/Tracking at Handling Limits

The increasing requirements for vehicle safety along with the impressive progress in vehicle actuation technologies have motivated manufacturers to equip vehicles with multiple control actuations that enhance handling and stability. Moreover, multiple control objectives arise in vehicle dynamics control problems, such as yaw rate control and rollover prevention, therefore, vehicle control problems can be defined as multi-actuation multi-objective vehicle control problems. Recently, the importance of integrating vehicle control systems has been highlighted in the literature. This integration allows us to prevent the potential conflicting control commands that could be generated by individual controllers. Existing studies on multi-actuated vehicle control offer a coordinated control design that shares the required control effort between the actuations. However, they mostly lack an appropriate strategy for considering the differences among vehicle actuations in their energy usage, capabilities, and effectiveness in any given vehicle states. Therefore, it is very important to develop a cost-performance strategy for optimally controlling multi-actuated vehicles. In this thesis, a prioritization model predictive control design is proposed for multi-actuated vehicles with multiple control objectives. The designed controller prioritizes the control actuations and control objectives based on, respectively, their advantages and their importance, and then combines the priorities such that a low priority actuation will not kick in unless a high priority objective demands it. The proposed controller is employed for several actuations, including electronic limited slip differential (ELSD), front/rear torque shifting, and differential braking. In this design, differential braking is engaged only when it is necessary, thus limiting or avoiding its disadvantages such as speed reduction and maintenance. In addition, the proposed control design includes a detailed analysis of the above-mentioned actuations in terms of modelling, control, and constraints. A new vehicle prediction model is designed for integrated lateral and roll dynamics that considers the force coupling effect and allows for the optimal control of front/rear torque distribution. The existing methods for ELSD control may result in chattering or unwanted oversteering yaw moments. To resolve this problem, a dynamic model is first designed for the ELSD clutch to properly estimate the clutch torque. This ELSD model is then used to design an intelligent ELSD controller that resolves the issues mentioned above. Experimental tests with two different vehicles are also carried out to evaluate the performance of the prioritization MPC controller in real-time. The results verify the capability of the controller in properly activating the control actuations with the designed priorities to improve vehicle handling and stability in different driving maneuvers. In addition, the test results confirm the performance of the designed ELSD model in ELSD clutch torque estimation and in enabling the controller to prevent unwanted oversteering yaw moments. The designed stability controller is extended to use for emergency collision avoidance in autonomous vehicles. This extension in fact addresses a local path planning/tracking problem with control objectives prioritized as: 1) collision avoidance, 2) vehicle stability, and 3) tracking the desired path. The controller combines a conservative form of torque/brake vectoring with front steering to improve the lateral agility and responsiveness of the vehicle in emergency collision avoidance scenarios. In addition, a contingency MPC controller is designed with two parallel prediction horizons - a nominal horizon and a contingency horizon - to maintain avoidance in identified road condition uncertainties. The performance of the model predictive controllers is evaluated in software simulations with high fidelity CarSim models, in which different sets of actuation configurations in various driving and road conditions are assessed. In addition, the effectiveness of the local path planning/tracking controller is evaluated in several emergency and contingency collision avoidance scenarios

A systematic approach to cooperative driving systems based on optimal control allocation

This dissertation proposes a systematic approach to vehicle dynamic control, where interaction between the human driver and on-board automated driving systems is considered a fundamental part of the overall control design. The hierarchical control system is to address motion control in three regions. First is normal driving, where the vehicle stays within the linear region of the tyre. Second is limit driving, where the vehicle stays within the nonlinear region of the tyre. Third is over-limit driving, where the driver demands go beyond the tyre force limits. The third case is addressed by a proposed control moderator (CM). The aim is to consider all three cases within a consistent hierarchical chassis control framework. The upper-level of the hierarchical control structure relates to both optimal vehicle control under normal and limit driving, and saturating driver demands for over-limit driving, these corresponding to a fully autonomous controller and driver assistance controller respectively. Model Predictive Control (MPC) is used as the core control technique for path following under normal driving conditions, and a Moderated Particle Reference (MPR) control strategy is proposed for the road departure mitigation during limit and over-limit driving. The MPR model is validated to ensure predictable and stable operation near the friction limits, maintaining controllability for curvature and speed tracking, which effectively limits demands on the vehicle while preserving the control interaction of the driver. In the next level of the hierarchical control structure, a novel control allocation (CA) approach based on pseudo-inverse method is proposed, while a general linearly constrained quadratic programming (CQP) approach is considered as a benchmark. From extended simulation experiments, it is found that the proposed Pseudo-Inverse CA (PICA) method can achieve a close match to CQP performance in normal driving conditions. This applies for multiple control targets (including path tracking, energy-efficient, etc.) and PICA is found to achieve improved performance in limit and over-limit driving, again addressing multiple control targets (including road departure mitigation, energyefficient, etc.). Furthermore, the PICA method shows its inherent advantages of achieving the same control performance with much less computational cost and is guaranteed to provide a feasible control target for the actuators to track during the highly dynamic driving scenarios. In addition, it can effectively solve the constrained optimal control problem with additional mechanical and electronic actuator constraints. Thus, the proposed PICA method, which uses Control Re-Allocation (making multiple calls to the pseudo-inverse operator) can be considered a feasible and novel alternative approach to control allocation, with advantages over the standard CQP method. Finally, in the lower-level of the hierarchical control structure, the desired tyre control variables are obtained through an analytical inverse tyre model and a sliding mode controller (SMC) is employed for the actuators to track the control target. The proposed hierarchical control system is validated with both driving simulator studies and from testing a real vehicle, considering a wide range of driving scenarios, from low-speed path tracking to safety-critical vehicle dynamic control. It therefore opens up a systematic approach to extended vehicle control applications, from fully autonomous driving to driver assistance systems and control objects from passenger cars to vehicles with higher centre of gravity (CoG) like SUVs, trucks and etc. . .