Synthesis and Analysis of an Active Independent Front Steering (AIFS) System

Technological developments in road vehicles over the last two decades have received considerable attention towards pushing the safe performance limits to their ultimate levels. Towards this goal, Active Front Steering (AFS) and Direct Yaw-moment Control (DYC) systems have been widely investigated. AFS systems introduce corrective steering angles to the conventional system in order to realize a target handling response for a given speed and steering input. An AFS system, however, may yield limited performance under severe steering maneuvers involving substantial lateral load shift and saturation of the inside tire-road adhesion. The adhesion available at the outer tire, on the other hand, would remain under-utilized. This dissertation explores effectiveness of an Active Independent Front Steering (AIFS) system that could introduce a corrective measure at each wheel in an independent manner. The effectiveness of the AIFS system was investigated firstly through simulation of a yaw-plane model of a passenger car. The preliminary simulation results with AIFS system revealed superior potential compared to the AFS particularly in the presence of greater lateral load shift during a high-g maneuver. The proposed concept was thus expected to be far more beneficial for enhancement of handling properties of heavy vehicles, which invariably undergo large lateral load shift due to their high center of mass and roll motion. A nonlinear yaw-plane model of a two-axle single-unit truck, fully and partially loaded with solid and liquid cargo, with limited roll degree-of-freedom (DOF) was thus developed to study the performance potentials of AIFS under a range of steering maneuvers. A simple PI controller was synthesized to track the reference yaw rate response of a neutral steer vehicle. The steering corrections, however, were limited such that none of the tires approach saturation. For this purpose, a tire saturation zone was identified considering the normalized cornering stiffness property of the tire. The controller strategy was formulated so as to limit the work-load magnitude at a pre-determined level to ensure sufficient tire-road adhesion reserve to meet the braking demand, when exists. Simulation results were obtained for a truck model integrating AFS and AIFS systems subjected to a range of steering maneuvers, namely: a J-turn maneuver on uniform as well as split-μ road conditions, and path change and obstacle avoidance maneuvers. The simulation results showed that both AFS and AIFS can effectively track the target yaw rate of the vehicle, while the AIFS helped limit saturation of the inside tire and permitted maximum utilization of the available tire-road adhesion of the outside tire. The results thus suggested that the performance of an AIFS system would be promising under severe maneuvers involving simultaneous braking and steering, since it permitted a desired adhesion reserve at each wheel to meet a braking demand during the steering maneuver. Accordingly, the vehicle model was extended to study the dynamic braking characteristics under braking-in-turn maneuvers. The simulation results revealed the most meritorious feature of the AIFS in enhancing the braking characteristics of the vehicle and reducing the stopping time during such maneuvers. The robustness of the proposed control synthesis was subsequently studied with respect to parameter variations and external disturbance. This investigation also explores designs of fail-safe independently controllable front wheels steering system for implementation of the AIFS concept

Investigation on maneuverability improvement of a four-wheel drive and rear-wheel steering system : numerical simulation analysis

X-by-wire technology is an advancement in the automotive industry and is recognized by many countries in recent years. It includes drive-by-wire (DBW) and steer-by-wire (SBW). DBW is available in two-wheel drive (2WD) and four-wheel drive (4WD) forms. 4WD has two forms: centralized motor drive and distributed motor drive. A centralized motor drive is to use the motor to replace the engine to provide power for the vehicle. The distributed motor drive is mainly based on the in-wheel motor, and the wheel is driven by the in-wheel motor to provide power for the vehicle. SBW has two forms: two-wheel steering (2WS) and four-wheel steering (4WS). It not only dramatically reduces the operating burden of the driver but also solves the problem that ordinary vehicles cannot perform 4WS. Usually, the lower maneuverability is easy to show on 2WS vehicles during vehicle turning. No matter when driving a vehicle on a narrow city road or parking, it is required to turn the steering wheel several times when the vehicle needs to steer. Moreover, the vehicle can be prone to understeer (US) or oversteer (OS) phenomena that occur when steering. The main purpose of this research is to simulate the steering performance of the vehicle by constructing a model of modern conventional vehicles and to solve the problems that may occur during vehicle cornering by applying an active 4WS control system to control the yaw rate. In this research, experiments of 2WS cornering at several constant speeds and steer angles were conducted using an actual experimental vehicle. A simulation model of the test car was constructed in MATLAB Simulink using nonlinear vehicle dynamics equations with the specification of the vehicle as the parameters. A PID control system was used in this simulation to control the rear-wheel steering angle in order to achieve 4WS. By comparing the simulation and the experimental result, it can be concluded that the nonlinear vehicle dynamics equation can be used to do the simulation of the vehicle motion. After verifying the vehicle dynamics equation, in order to verify whether the time of rotating the steering wheel will affect the motion of the vehicle, this study simulated two different times to complete the rotation of the wheel which is 2 seconds and 25 seconds with the front steering angle is 10 degrees. The results show that no matter whether the time of steering wheel rotation is fast or slow, it does not affect the speed of the vehicle's US and OS phenomenon. By simulating the cornering situation of the vehicle speeds from 10km/h to 80 km/h in the 10km/h increment. It is concluded that the vehicle will occur US phenomenon when the vehicle turning speed is lower around 20km/h; when the vehicle corners with a speed higher than 50km/h, the vehicle will have an OS phenomenon happen. After applying the 4WS system, the OS and US problems are solved efficiently. Although the vehicle is turning at a speed of 80km/h, steady-state cornering (SSC) can still be achieved. After applying the PID control system, most of the cornering can be controlled. except when the wheels rotate to 10° in only two seconds and the vehicle speed is greater than 60km/h which is the vehicle is out of control in a very short time, the PID control system cannot make the rear wheels have an appropriate steering angle to make the vehicle have an SSC. In short, this study solved almost all US and OS phenomena that can occur in 2WS vehicles by applying the 4WS system

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

Control of vehicle lateral dynamics based on longitudinal wheel forces

Trends show that on board vehicle technology is becoming increasingly complex and that this will continue to be the case. This complexity has enabled both driver assistance systems and fully automatic systems to be introduced. Driver assistance systems include anti-lock braking and yaw rate control, and these differ from fully automatic systems which include collision avoidance systems, where control of the car may be taken away from the driver. With this distinct difference in mind, this work will focus on driver assist based systems, where emerging technology has created an opportunity to try and improve upon the systems which are currently available. This work investigates the ability to simultaneously control a set of two lateral dynamics using primarily the longitudinal wheels forces. This approach will then be integrated with front wheel steering control to assess if any benefits can be obtained. To aid this work, three different vehicle models are available. A linear model is derived for the controller design stage, and a highly nonlinear validated model from an industrial partner is available for simulation and evaluation purposes. A third model, which is also nonlinear, is used to integrate the control structures with a human interface test rig in a Hardware in the Loop (HiL) environment, which operates in real-time. Frequency based analysis and design techniques are used for the feedback controller design, and a feedforward based approach is used to apply a steering angle to the vehicle model. Computer simulations are initially used to evaluate the controllers, followed by evaluation via a HiL setup using a test rig. Using a visualisation environment in Matlab, this interface device allows driver interaction with the controllers to be analysed. It also enables driver reaction without any controllers present to be compared directly with the controller performance whilst completing the test manoeuvres. Results show that during certain manoeuvres, large variations in vehicle velocity are required to complete the control objective. However, it can be concluded from both the computer simulation and HiL results that simultaneous control of the lateral dynamics, based on the longitudinal wheel forces can be achieved using linear control methods

Actuators for Intelligent Electric Vehicles

This book details the advanced actuators for IEVs and the control algorithm design. In the actuator design, the configuration four-wheel independent drive/steering electric vehicles is reviewed. An in-wheel two-speed AMT with selectable one-way clutch is designed for IEV. Considering uncertainties, the optimization design for the planetary gear train of IEV is conducted. An electric power steering system is designed for IEV. In addition, advanced control algorithms are proposed in favour of active safety improvement. A supervision mechanism is applied to the segment drift control of autonomous driving. Double super-resolution network is used to design the intelligent driving algorithm. Torque distribution control technology and four-wheel steering technology are utilized for path tracking and adaptive cruise control. To advance the control accuracy, advanced estimation algorithms are studied in this book. The tyre-road peak friction coefficient under full slip rate range is identified based on the normalized tyre model. The pressure of the electro-hydraulic brake system is estimated based on signal fusion. Besides, a multi-semantic driver behaviour recognition model of autonomous vehicles is designed using confidence fusion mechanism. Moreover, a mono-vision based lateral localization system of low-cost autonomous vehicles is proposed with deep learning curb detection. To sum up, the discussed advanced actuators, control and estimation algorithms are beneficial to the active safety improvement of IEVs

Active neuro-fuzzy integrated vehicle dynamics controller to improve the vehicle handling adn stability at complicated maneuvers

With the recent advancements in vehicle’s industry, driving safety in passenger vehicles is considered one of the key issues in designing any vehicle. According to other studies Electronic Stability Control (ESC) is considered to be the greatest road safety innovation since the seatbelt. Yet ESC has its drawbacks, that encouraged the development of other stability systems to correct or compensate these draw backs. But to efficiently make up for the ESC problems the integration of various control systems is needed, which is a pretty complicated task on its own. Lately, solving this stability problem became a hot research topic accompanied by the market demands for improving the available stability systems. Therefore, this thesis aims to add an innovative approach to help improve the vehicle stability. This approach consists of an intelligent algorithm that collects data about the vehicle characteristics and behavior. Then it uses an Artificial Neural Network to construct a fuzzy logic control system through learning from the optimum control values that was generated beforehand by the intelligent algorithm. This way, the proposed controller didn’t depend only on experts’ knowledge like the other controllers presented in the literature. This makes the controller more generic and reliable which is a very important aspect in designing a safety critical controller, like the presented one, where any fault in it can lead to a fatal accident. Also using the technique of using an Artificial Neural Network to construct a fuzzy logic control allows benefiting from the learning and autoautoadaption capability of neural networks and the smooth controlling performance that fuzzy logic controllers offers. Simulations results show the effectiveness of the proposed controller for improving the vehicle stability in different driving maneuvers. Where the controller’s results were compared to an uncontrolled vehicle and another vehicle controlled by a controller from the literature. -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Cuando un vehículo entra en una curva a alta velocidad, la aceleración lateral producida hace que el vehículo tienda a ser más inestable y menos controlable desde el punto de vista del conductor. Esta inestabilidad, podría conllevar un comportamiento no deseado del vehículo, como el sub-viraje o el sobre-viraje, que pueden llevar al vehículo a salirse de su curso previsto o que vuelque. Además, las estadísticas concluyen que la inestabilidad lateral del vehículo es causa de accidentes de fatales consecuencias. Para hacer frente a este problema, se han propuesto varios sistemas de control, con el objetivo de generar una acción contraria que lleve de nuevo al vehículo a su curso deseado. Estos sistemas pretenden alterar de una manera u otra las fuerzas centrífugas del neumático con el fin de producir fuerzas de compensación que ayuden a mantener el control lateral del vehículo. Estos controladores presentan estrategias de control diferentes: algunos intentan afectar directamente a los ángulos de dirección de los neumáticos, otros inciden en las fuerzas longitudinales de los neumáticos para crear un momento de guiñaada alrededor del eje vertical del vehículo, y por último, otros intentan afectar a la distribución de la carga vertical entre los neumáticos. Por ello, debido a la diferencia de las características de cada uno de estos sistemas, sus capacidades de controlar también difieren. Sin desmerecer a ninguno de ellos, algunos demuestran mayor eficacia en situaciones de inestabilidad suaves; otros lo son cuando el vehículo llega a sus límites de adhesión, y los hay cuando la aceleración lateral supera un cierto valor. Por esta razón, se recomienda el uso de más de un sistema de control para beneficiarse de las ventajas de sus diferentes conceptos de control. Sin embargo, la combinación de más de un controlador de estabilidad de un vehículo, no es tarea fácil, dado que podrían producirse conflictos entre los diferentes controladores, así como la superposición de los diferentes objetivos de control. Adicionalmente, una simple combinación podría llevar a una mayor complejidad del hardware y el software usados, debido a la posible repetición de sensores y actuadores, y en consecuencia a una complejidad de cables de conexión. Por ello, se han propuesto sistemas de Dinámica de Vehículos de Control Integral (IVDC), para proporcionar una integración cuidadosamente diseñada con el objetivo de coordinar los diferentes sistemas de control del chasis. De esta manera, los conflictos de control podrían ser eliminados, y los resultados podrían reforzarse aún más mediante tal combinación. Igualmente el coste y la complejidad del sistema podrían reducirse debido al posible uso compartido de sensores, actuadores, unidades de control y cables. Recientemente, los sistemas de IVDC han sido un tema de investigación recurrente, existiendo distintos sistemas en la literatura que han intentado controlar varias combinaciones de los citados controladores utilizando una variedad de técnicas de control, muchos de los cuales han mostrado resultados prometedores en la mejora del manejo del vehículo a través de los resultados de simulaciones. No obstante, estos sistemas eran manualmente diseñados y probados en un número limitado de maniobras y condiciones. Además, han sido testados en las mismas maniobras utilizadas para su dise˜no y, por tanto, su fiabilidad y previsibilidad son cuestionables. Por otra parte, los sistemas de control de estabilidad del vehículo son considerados como sistemas de seguridad crítica, donde cualquier error podría causar un accidente fatal. De este modo, como consecuencia de la imprecisión humana, un controlador diseñado manualmente que ha sido desarrollado a través de pruebas de situación limitada, es propenso a errores que generan deficiencias en ciertas zonas de control o a inexactitudes en las decisiones de los valores de control. Por otra parte, la selección manual del margen de control dedicado a cada sub-sistema integrado no asegura la optimización de las capacidades de los controladores. Además, dado que estos controladores son diseñados por el hombre, cualquier variación de las características del modelo del vehículo, como por ejemplo algo tan sencillo como el cambio en la rigidez de la suspensión, necesitaría de intervención humana para volver a calibrar o volver a ajustar manualmente el sistema con el objetivo de adaptarse a la variación realizada. Por lo tanto, en esta tesis se intentará reemplazar el conocimiento humano y los sistemas diseñados manualmente, por un sistema automatizado e inteligente, que autoconstruye el sistema de control sin intervención humana. Este método utilizará una red neuronal inteligente que aprende los valores óptimos de control a través de un algoritmo extenso de minería de datos. En consecuencia, se autoconstruye un controlador de lógica difusa que corrige la estabilidad del vehículo a través de un sistema activo de corrección de la entrada al volante y un sistema de control de ángulo de guiñada mediante los frenos. Las entradas de control de estos sistemas serán la velocidad del ángulo de guiñada y el ángulo de deslizamiento lateral, siendo los controladores más eficaces presentados en la literatura

The influence of the sideslip target on the performance of vehicles with actively controlled handling

The influence of sideslip on the handling capability of a four wheeled vehicle is investigated. Both nonlinear, steady-state and linear, transient analyses are conducted on simple models in order to understand how the geometric and inertial effects of sideslip control influence the maneuvering capability of the vehicle. Nonlinear performance analyses confirm the findings of the literature, that constant sideslip angle at the centre of mass is required if it is desired to maintain consistent vehicle 'balance' with increasing lateral acceleration, and the reason for this is explained using simple mathematics. Analyses of energy flow between the power source and the various sinks of the vehicle show that for a typical modem vehicle, the power dissipated in a steady turn near the limiting lateral acceleration is approximately comparable in magnitude to that dissipated by aerodynamic drag near the maximum speed of the vehicle. Additionally, it shown that whenever brake control, rather than steering control, is employed to generate a yawing moment, the component of dissipated energy associated with this yaw demand is larger by at least an order of magnitude. It is concluded that whenever the required dynamic behaviour can be delivered by means of steering alone pure steering control should be preferred over the use of direct yaw control. This suggests that direct yaw control should only be used when the limit of the envelope of the steered vehicle has been reached. Transient analyses of sudden turn-in events are then undertaken. The assumption is that the driver wishes to maximise the lateral displacement of the vehicle as quickly as possible. Vehicle handling models with A WS are linearised and discretised, and Linear Progranuning is used to identifY the optimal turn-in maneuver. The objective is to understand how to make a vehicle perform well against such a target without any use of any energy-dissipating direct yaw control. It is observed that the optimal controls usually involve an immediate step to the limiting force that the front axle is able to deliver. It is shown that for vehicles with yaw dynamics where this input does not lead to saturation of the rear tyres, the transient performance is totally insensitive to changes in the enforced sideslip control. The form of this optimal force input is then used in a further mathematical analysis of the optimal obstacle avoidance maneuver. It is shown that in the case mentioned above, where sufficient friction is available at the rear axle, the time taken to build up lateral acceleration and yaw rate for a turn is a simple function of the geometric and inertial properties of the vehicle, and unrelated to rear tyre cornering stiffness, rear camber or rear steering control. It is shown also shown that for an equal level of limit over- or under-steer, 2WS vehicles that are limit over-steering are able to turn in more quickly than those which are limit under-steering, since the excess friction is available at the front axle, and can be used during the turn-in phase. Further, it is shown that both commonly adopted sideslip targets for 4WS vehicles and responses that often result from 2WS vehicles can easily be 'incompatible' with the handling envelope of a steered vehicle from an optimal obstacle avoidance point of view. This means that for some vehicles, strict enforcement of such sideslip targets directly increases the time taken to transfer such a vehicle to the limiting lateral acceleration. This limit of 'compatibility' of the sideslip target and vehicle envelope is confirmed analytically. It is then shown, that the zero sideslip target which is commonly adopted for A WS vehicles in the literature, and which was previously shown to be the ideal for consistent vehicle stability and 'balance', is only able to deliver the optimal turn-in behaviour when the underlying vehicle has a limit-neutral or limit under-steering balance. Further, the zero sideslip target requires a strongly limit under-steering balance if the sideslip target is to be maintained when the vehicle is rnaneuvered from turning quickly in one direction to turning quickly in the other without compromising the time taken to complete the maneuver. However, it is also shown that either a controlled front differential, or front axle direct yaw-moment control are each able to extend the envelope of the vehicle in the necessary direction that maintaining zero sideslip throughout such transients may become feasible, albeit at an energy cost that increases as the vehicle is maneuvered more rapidly. Additionally, an alternative sideslip target is presented, that allows optimal maneuvering to take place whilst the sideslip target is simultaneously maintained, without requiring the intervention of controlled differentials or direct yaw control.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

GVSU Press Releases, 1978

A compilation of press releases for the year 1978 submitted by University Communications (formerly News & Information Services) to news agencies concerning the people, places, and events related to Grand Valley State University