81 research outputs found
Robust estimation of Ackerman angles for front-axle steering vehicles
The multiple benefits of automating steering in agricultural vehicles have resulted in various autoguidance systems commercially available, most of them relying on satellite-based positioning. However, the fact that farm equipment is typically oversized, heavy, and highly powered poses serious challenges to automation in terms of safety and reliability. The objective of this research is to improve the reliability of front-wheel feedback signals as a preliminary stage in the development of stable steering control systems. To do so, the angle turned by each front wheel of a conventional tractor was independently measured by an optical encoder and fused to generate the Ackerman feedback angle. The proposed fusion algorithm analyzes the consistency of each signal with time and checks the coherence between left and right front wheels according to the vehicle steering mechanism. Field experiments demonstrated the benefits of using redundant sensors coupled through logic algorithms for estimating Ackerman angles as the harsh conditions of off-road environments often resulted in the unreliable performance of electronic devices.Sáiz Rubio, V.; Rovira Más, F.; Chatterjee, I.; Molina Hidalgo, JM. (2013). Robust estimation of Ackerman angles for front-axle steering vehicles. Artificial Intelligence Research. 2(2):18-28. doi:10.5430/air.v2n2p18S18282
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
Wheel speed distribution control and its effect on vehicle handling
The current work aims at bridging the gap between the current vehicle handling characteristics and the future demands of higher vehicle handling performance, required to guarantee higher safety and facilitate the application of autonomous driving, platooning and automated highways systems. For this task a state 'of the art vehicle chassis control system known as "Wheel Speed Distribution Control" (WSDC) has been proposed. WSDC in principle relies on controlling the vehicle driven wheel speeds to enforce better vehicle handling performance. The WSDC system capacity has been investigated using numerical simulation. Tberefore, an innovative vehicle handling simulation model has been developed from first principles. It employs the Magic Formula (MF) tyre model for combined slip, has 23 degrees of freedom and includes more than 60 vehicle handling parameters. The vehicle handling model has been developed using the novel Cartesian Geometric Translation (CGf) technique which employs geometry, trigonometry, Cartesian coordinates and finite difference approximation in the time domain to facilitate development of high speed models. The model has been built using the BASIC'O programming code in the DOS'O environment and optimised to meet the novel Model Predictive Control (MPC) based feedforward WSDC yaw rate controller requirements, such as small code size (less than 35 kb) and processing speed faster than real time. The simulation results validated the WSDC principles as it showed the capacity of WSDC to enforce the desired yaw rates, with acceptable driven wheel longitudinal forces. To put WSDC into practice,an original hardware" Wheel Speed Distribution Differential" (WSDD) design has been developed and optimised for lower speed, torque, power,production and maintenance requirements.It has the capacity to precisely differentiate the driven wheels speed under the influence of a DC motor with relatively small power requirements. It has linear speed and torque characteristics which facilitate its control. It also has been developed to allow many beneficial differential modes. The simulation results of the whole WSDC system have clearly demonstrated that it can in fact achieve its development target of feasibly enhancing vehicle handling performance.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Design and Simulation of Small Space Parallel Parking Fuzzy Controller
Based on the nonlinearity and time-variation of automatic parking path tracking control system, we use fuzzy control theories and methods to explore the control rules to improve fuzzy controllers and design an automobile steering controller. Then we build the simulation experiment platform of an automobile in Simulink to simulate the reversing settings of parallel parking. This paper adopts the Mamdani control rules; the membership function is the Gauss function. This paper verifies the fuzzy controller's kinematic model and the advantages of fuzzy control rules. Simulation results show that the design of the controller allows the automobile to stop into the parking space smaller than the space obtained by planning path, and automatic parking becomes possible in the parking plot. The control system is characterized by small tracking error, fast response and high reliability
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An Investigation of Higher Capacity Urban Freight Vehicles
Studies have shown that increasing the capacity of Heavy Goods Vehicles is one of the most effective ways of reducing fuel consumption per tonne-kilometre of freight moved, with consequent reductions in greenhouse and noxious emissions. Some of the disadvantages of larger vehicles are more pronounced in urban environments, including safety of other road users, and reduced manoeuvrability. This thesis discusses technologies for improving safety of vulnerable road users, and frameworks for assessing the maximum size of urban freight vehicles.
An overview of the freight industry is provided in Chapter 1, with a focus on maximising capacity as a method for reducing emissions. Chapter 2 focusses on the safety of vulnerable road users, through development of a camera-based detection system for cyclists, which is essential for a predictive collision avoidance system. The proposed system is accurate to within 10 cm at distances of greater than 1 m from the vehicle, but suffers from loss of accuracy at close range, and in poor lighting conditions.
The logistics of urban freight operations are analysed in Chapter 3, including a comparison between two supermarket home delivery operations, and an analysis of refuse collection schedules. A framework is proposed for selecting an optimum vehicle size for a multi-drop operation, given reductions in driving distance and time spent on other procedures. A potential capacity increase of 80% is demonstrated, requiring a 50% reduction in driving distance, and automation of certain procedures.
Chapters 4 to 6 propose a novel framework for assessing the optimum size of Heavy Goods Vehicles, according to the limits of their manoeuvrability. This method is based on simulation of vehicles attempting a library of real-world manoeuvres. Simulation models are described in Chapter 4, and path planning algorithms in Chapter 5. The framework is evaluated on three case studies: a 4.25 t grocery delivery vehicle, a 44 t articulated refuse collection vehicle, and a 44 t general urban vehicle with rear axle steering. A range of potential higher capacity vehicles are proposed in Chapter 6 for those applications
The impact of rear axle steering on manoeuvrability is also considered in detail in Chapter 6. It is shown that the use of rear axle steering does not always allow the use of a longer vehicle, because a rear axle steered vehicle cannot compromise between cut-in and tailswing in the way a conventional vehicle can. However, the use of rear axle steering allows reduction in both tyre wear and rear axle load limits, which permits greater vehicle fill before rear axle loads are exceeded.
These results are compared, in Chapter 7, to an alternative method for modelling manoeuvrability (Performance-Based Standards). Finally, Chapter 8 presents some concluding remarks and recommendations for future work, including investigation of an improved cyclist detection system fusing cameras and ultrasonic sensors, and increased development of the manoeuvrability models to more accurately reflect real driving.This work was supported by the EPSRC, as well as the Cambridge Vehicle Dynamics Consortium, and the Centre for Sustainable Road Freigh
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
Steering Controller for Intelligent Vehicle
In the last years, the development of autonomous vehicles has arisen a big interest in
the big industry of the automotive sector. In addition to several car manufacturing
companies, many electronics enterprises are trying to join the market, and a big deal of
research is being done in this field. This thesis contributes to said research by developing
a steering controller for an autonomous Unmaned Ground Vehicle (UGV).
Due to system specifics, the proposed controller must adapt to the already sealed
low-level control of the UGV and function externally to it. The proposed controller
is tailored as a deadband compensator, set to overcome the steering motor's internal
proportional-integral-derivative (PID)'s steady state error constrains, and prompt the
vehicle to respond accurately to the received reference angle. This compensator is created
as a C++ code and implemented through Robot Operating System (ROS) architecture.
After the results from the experimental work have been analyzed, the outcome is that
the compensator does bring benefit in terms of accurately following the reference steering
angle. Qualitative results show that once the compensator is implemented, most of the
desired angles are achieved, while only a few cause the system to oscillate. Quantitative
results do not present such a favorable outcome, with an improvement of around 9%.
This might be due to the result being measured as the mean absolute error instead of the
steady state error.En los últimos años, el desarrollo de vehículos autónomos ha generado un gran interés
por parte de las grandes empresas del sector automotor. Además de varias compañías
de fabricación de coches, muchas empresas de electrónica están intentando entrar al
mercado, y se está realizando gran cantidad de investigación en este campo. Este trabajo
contribuye a la investigación mediante el desarrollo de un controlador de dirección para
un Vehículo Terrestre No Tripulado (UGV) autónomo.
Debido a las particularidades del sistema, el controlador propuesto debe adaptarse
al control de bajo nivel preestablecido del UGV, y funcionar externamente al mismo.
El controlador propuesto se diseña como un compensador de deadband (zona muerta o
zona neutral), establecido para vencer las restricciones del controlador PID interno del
motor, e instar al vehículo a responder con exactitud al ángulo de referencia recibido. El
compensador es programado en C++ e implementado a través de arquitectura ROS.
Tras analizar los resultados del trabajo experimental, se concluye que el compensador
es beneficioso en cuanto a seguir la referencia del ángulo de dirección con exactitud. Los
resultados cualitativos muestran que una vez implementado el compensador, la mayoría
de los ángulos son alcanzados, y solo unos pocos provocan oscilaciones en el sistema. Los
resultados cuantitativos no presentan un resultado tan favorable, con una mejora entorno
al 9%. Esto puede ser debido al uso del error absoluto medio como métrica en lugar del
error en estado estacionario.Ingeniería en Tecnologías Industriale
DESIGN OF A SEMI-ACTIVE STEERING SYSTEM FOR A PASSENGER CAR
This thesis presents research into an improved active steering system technology for a
passenger car road vehicle, based on the concept of steer-by-wire (SBW) but possessing
additional safety features and advanced control algorithms to enable active steering
intervention. An innovative active steering system has been developed as 'Semi-Active
Steering' (SAS) in which the rigid steering shaft is replaced with a low stiffness resilient
shaft (LSRS). This allows active steer to be performed by producing more or less steer angle
to the front steered road wheels relative to the steering wheel input angle. The system could
switch to either being 'active' or 'conventional' depending on the running conditions of the
vehicle; e.g. during normal driving conditions, the steering system behaves similarly to a
power-assisted steering system, but under extreme conditions the control system may
intervene in the vehicle driving control. The driver control input at the steering wheel is
transmitted to the steered wheels via a controlled steering motor and in the event of motor
failure, the LSRS provides a basic steering function. During operation of the SAS, a reaction
motor applies counter torque to the steering wheel which simulates the steering 'feel'
experienced in a conventional steering system and also applies equal and opposite counter
torque to eliminate disturbance force from being felt at the steering wheel during active
control operation.
The thesis starts with the development of a mathematical model for a cornering road
vehicle fitted with hydraulic power-assisted steering, in order to understand the relationships
between steering characteristics such as steering feel, steering wheel torque and power boost
characteristic. The mathematical model is then used to predict the behaviour of a vehicle
fitted with the LSRS to represent the SAS system in the event of system failure. The
theoretical minimum range of stiffness values of the flexible shaft to maintain safe driving
was predicted.
Experiments on a real vehicle fitted with an LSRS steering shaft simulator have been
conducted in order to validate the mathematical model. It was found that a vehicle fitted with
a suitable range of steering shaft stiffness was stable and safe to be driven. The mathematical
model was also used to predict vehicle characteristics under different driving conditions
which were impossible to conduct safely as experiments.
Novel control algorithms for the SAS system were developed to include two main criteria,
viz. power-assistance and active steer. An ideal power boost characteristic curve for a
hydraulic power-assisted steering was selected and modified and a control strategy similar to
Steer-by-Wire (SBW) was implemented on the SAS system.
A full-vehicle computer model of a selected passenger car was generated using
ADAMS/car software in order to demonstrate the implementation of the proposed SAS
system. The power-assistance characteristics were optimized and parameters were determined
by using an iteration technique inside the ADAMS/car software. An example of an open-loop
control system was selected to demonstrate how the vehicle could display either under-steer
or over-steer depending on the vehicle motion.
The simulation results showed that a vehicle fitted with the SAS system could have a
much better performance in terms of safety and vehicle control as compared to a conventional
vehicle. The characteristics of the SAS system met all the requirements of a robust steering
system. It is concluded that the SAS has advantages which could lead to its being safely fitted
to passenger cars in the future.
Keywords: steer-by-wire, active steering, innovative, power-assisted steering, steering
control, flexible shaft, steering intervention, system failure, safety features
Compendium in Vehicle Motion Engineering
This compendium is written for the course “MMF062 Vehicle Motion Engineering” at Chalmers University of Technology. The compendium covers more than included in that course; both in terms of subsystem designs and in terms of some teasers for more advanced studies of vehicle dynamics. Therefore, it is also useful for the more advanced course “TME102 Vehicle Modelling and Control”.The overall objective of the compendium is to educate vehicle dynamists, i.e., engineers that understand and can contribute to development of good motion and energy functionality of vehicles. The compendium focuses on road vehicles, primarily passenger cars and commercial vehicles. Smaller road vehicles, such as bicycles and single-person cars, are only very briefly addressed. It should be mentioned that there exist a lot of ground-vehicle types not covered at all, such as: off-road/construction vehicles, tracked vehicles, horse wagons, hovercrafts, or railway vehicles.Functions are needed for requirement setting, design and verification. The overall order within the compendium is that models/methods/tools needed to understand each function are placed before the functions. Chapters 3-5 describes (complete vehicle) “functions”, organised after vehicle motion directions:\ub7\ua0\ua0\ua0\ua0\ua0\ua0\ua0\ua0 Chapter 3:\ua0Longitudinal\ua0dynamics\ub7\ua0\ua0\ua0\ua0\ua0\ua0\ua0\ua0 Chapter 4:\ua0Lateral\ua0dynamics\ub7\ua0\ua0\ua0\ua0\ua0\ua0\ua0\ua0 Chapter 5:\ua0Vertical\ua0dynamicsChapter 1 introduces automotive industry and the overall way of working there and defines required pre-knowledge from “product-generic” engineering, e.g. modelling of dynamic systems.Chapter 2 also describes the subsystems relevant for vehicle dynamics:• Wheels and Tyre\ua0• Suspension\ua0• Propulsion\ua0• Braking System\ua0• Steering System\ua0• Environment Sensing Syste
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