Optimization And Control Of Semi Active Suspension System For Off Road Vehicles

This study evaluates the dynamic response of three semi-active control policies as analyzed on a several off-road models. Two-axle 7DOF, three-axle 9DOF and four-axle 11DOF full vehicle system was developed to evaluate skyhook, groundhook, and hybrid controls. As well as exploring the relative benefits of each of these controllers, the performance of each semi-active controller was compared to the performance of conventional passive system. Each control policy is evaluated for its control performance under three different base excitations: step, bump and random. Corresponding to the bump and random inputs, peak-to-peak, RMS and frequency responses are considered for each control policy along with passive system. Specifically, sprung mass (heavy, pitch and roll acceleration), suspension and tire deflection. A comparison between different suspension systems were examined using half vehicle model and step input used to generate the time domain values of settling time and PTP acceleration for hybrid control policy and compared to fully active and passive systems using two-axle half vehicle model. Furthermore, Due to the importance of ride comfort for off-road vehicles, minimizing the peak-to-peak of the vertical, pitch and roll acceleration and reducing the settling time would lead to better ride comfort. In solving this problem, the step input was used for the optimization of a two-axle full vehicle's semi-active suspension system parameters with respect to ride comfort and handling. Genetic algorithm optimization technique is developed and used. Step input also used to generate the time domain and frequency domain responses of the four-axle full vehicle model. Reponses of sprung mass, suspension and tired deflection are obtained. Results of this study show that semi-active control offers benefits beyond those of conventional passive system. Further, traditional skyhook control is shown to be better in improving the vehicle body acceleration PTP, RMS and PSD responses. The groundhook control is shown to be better in controlling the tire deflection. Hybrid as a combination of both control policies skyhook and groundhook, shows to be better compromise in improving ride comfort and handling of the vehicle compared to passive system in all cases. Result shows also, that GA has consistently found near-optimal solutions within specified parameters ranges for several independent runs. Ride comfort improved without reducing the handling of the vehicle.

Semi-Active Suspension Control Design for Vehicles presents a comprehensive discussion of designing control algorithms for semi-active suspensions. It also covers performance analysis and control design. The book evaluates approaches to different control theories, and it includes methods needed for analyzing and evaluating suspension performances, while identifying optimal performance bounds. The structure of the book follows a classical path of control-system design; it discusses the actuator or the variable-damping shock absorber, models and technologies. It also models and discusses the vehicle that is equipped with semi-active dampers, and the control algorithms. The text can be viewed at three different levels: tutorial for novices and students; application-oriented for engineers and practitioners; and methodology-oriented for researchers. The book is divided into two parts. The first part includes chapters 2 to 6, in which fundamentals of modeling and semi-active control design are discussed. The second part includes chapters 6 to 8, which cover research-oriented solutions and case studies. The text is a comprehensive reference book for research engineers working on ground vehicle systems; automotive and design engineers working on suspension systems; control engineers; and graduate students in control theory and ground vehicle systems. Appropriate as a tutorial for students in automotive systems, an application-oriented reference for engineers, and a control design-oriented text for researchers that introduces semi-active suspension theory and practice Includes explanations of two innovative semi-active suspension strategies to enhance either comfort or road-holding performance, with complete analyses of both Also features a case study showing complete implementation of all the presented strategies and summary descriptions of classical control algorithms for controlled dampers

Semi-active Suspension Control provides an overview of vehicle ride control employing smart semi-active damping systems. These systems are able to tune the amount of damping in response to measured vehicle-ride and handling indicators. Two physically different dampers (magnetorheological and controlled-friction) are analysed from the perspectives of mechatronics and control. Ride comfort, road holding, road damage and human-body modelling are studied. Mathematical modelling is balanced by a large and detailed section on experimental implementation, where a variety of automotive applications are described offering a well-rounded view. The implementation of control algorithms with regard to real-life engineering constraints is emphasised. The applications described include semi-active suspensions for a saloon car, seat suspensions for vehicles not equipped with a primary suspension, and control of heavy-vehicle dynamic-tyre loads to reduce road damage and improve handling.

For the past several decades there have been many attempts to improve suspension performance due to its importance within vehicle dynamics. The suspension system main functions are to connect the chassis to the ground, and to isolate the chassis from the ground. To improve upon these two functions, large amounts of effort are focused on two elements that form the building blocks of the suspension system, stiffness and damping. With the advent of new technologies, such as variable dampers, and powerful microprocessors and sensors, suspension performance can be enhanced beyond the traditional capabilities of a passive suspension system. Recently, Yin et al. [1, 2] have developed a novel dual chamber pneumatic spring that can provide tunable stiffness characteristics, which is rare compared to the sea of tunable dampers. The purpose of this thesis is to develop a controller to take advantage of the novel pneumatic spring's functionality with a tunable damper to improve vehicle dynamic performance. Since the pneumatic spring is a slow-acting element (i.e. low bandwidth), the typical control logic for semi-active suspension systems are not practical for this framework. Most semi-active controllers assume the use of fast-acting (i.e. high bandwidth) variable dampers within the suspension design. In this case, a lookup table controller is used to manage the stiffness and damping properties for a wide range of operating conditions. To determine the optimum stiffness and damping properties, optimization is employed. Four objective functions are used to quantify vehicle performance; ride comfort, rattle space (i.e. suspension deflection), handling (i.e. tire deflection), and undamped sprung mass natural frequency. The goal is to minimize the first three objectives, while maximizing the latter to avoid motion sickness starting from 1Hz and downward. However, these goals cannot be attained simultaneously, necessitating compromises between them. Using the optimization strength of genetic algorithms, a Pareto optima set can be generated to determine the compromises between objective functions that have been normalized. Using a trade-off study, the stiffness and damping properties can be selected from the Pareto optima set for suitability within an operating condition of the control logic. When implementing the lookup table controller, a practical method is employed to recognize the road profile as there is no direct method to determine road profile. To determine the road profile for the lookup table controller, the unsprung mass RMS acceleration and suspension state are utilized. To alleviate the inherent flip-flopping drawback of lookup table controllers, a temporal deadband is employed to eliminate the flip-flopping of the lookup table controller. Results from the semi-active suspension with tunable stiffness and damping show that vehicle performance, depending on road roughness and vehicle speed, can improve up to 18% over passive suspension systems. Since the controller does not constantly adjust the damping properties, cost and reliability may increase over traditional semi-active suspension systems. The flip-flopping drawback of lookup table controllers has been reduced through the use of a temporal deadband, however further enhancement is required to eliminate flip-flopping within the control logic. Looking forward, the novel semi-active suspension has great potential to improve vehicle dynamic performance especially for heavy vehicles that have large sprung mass variation, but to increase robustness the following should be considered: better road profile recognition, the elimination of flip-flopping between suspension states, and using state equations model of the pneumatic spring within the vehicle model for optimization and evaluation.

This book focuses on most recent theoretical findings on control issues for active suspension systems. The authors first introduce the theoretical background of active suspension control, then present constrained H∞ control approaches of active suspension systems in the entire frequency domain, focusing on the state feedback and dynamic output feedback controller in the finite frequency domain which people are most sensitive to. The book also contains nonlinear constrained tracking control via terminal sliding-mode control and adaptive robust theory, presenting controller design of active suspensions as well as the reliability control of active suspension systems. The target audience primarily comprises research experts in control theory, but the book may also be beneficial for graduate students alike.

Featuring contributions from industry leaders in their respective fields, this volume presents comprehensive, authoritative coverage of all the major issues involved in road vehicle dynamic behavior. It begins with a short history of road and off-road vehicle dynamics followed by thorough, detailed state-of-the-art chapters on modeling, analysis and optimization in vehicle system dynamics, vehicle concepts and aerodynamics, pneumatic tires and contact wheel-road/off-road, modeling vehicle subsystems, vehicle dynamics and active safety, man-vehicle interaction, intelligent vehicle systems, and road accident reconstruction and passive safety.

This book deals with the analysis of off-road vehicle dynamics from kinetics and kinematics perspectives and the performance of vehicle traversing over rough and irregular terrain. The authors consider the wheel performance, soil-tire interactions and their interface, tractive performance of the vehicle, ride comfort, stability over maneuvering, transient and steady state conditions of the vehicle traversing, modeling the aforementioned aspects and optimization from energetic and vehicle mobility perspectives. This book brings novel figures for the transient dynamics and original wheel terrain dynamics at on-the-go condition.

Vehicles handling and ride comfort are essential subject because these vehicles operate at different environments. Improving the comfortability enables the drivers to derive for a long time at critical situations with full activity. This work deals with dynamics and control policies analysis of semi-active suspension systems for off-road vehicles. Comprehensive comparison on three different configurations; 2-axle, 3-axle and 4-axle half-vehicle models were conducted to analyze the effect of using semi-active control policies. The application of several control policies of semi-active suspension system, namely skyhook; ground-hook and hybrid controls have been analyzed and compared with passive systems. Sprung mass acceleration, suspension deflection and tyre deflection responses were analyzed for measurements of ride quality and road handling. Analysis in frequency domain transfer function, time domain transient state and time domain steady state were conducted on each of the models.

With the new advancements in the vibration control strategies and controllable actuator manufacturing, the semi-active actuators (dampers) are finding their way as an essential part of vibration isolators, particularly in vehicle suspension systems. This is attributed to the fact that in a semi-active system, the damping coefficients can be adjusted to improve ride comfort and road handling performances. The currently available semi-active damper technologies can be divided into two main groups. The first uses controllable electromagnetic valves. The second uses magnetorheological (MR) fluid to control the damping characteristics of the system. Leading automotive companies such as General Motors and Volvo have started to use semi-active actuators in the suspension systems of high-end automobiles, such as the Cadillac Seville and Corvette, to improve the handling and ride performance in the vehicle. But much more research and development is needed in design, fabrication, and control of semi-active suspension systems and many challenges must be overcome in this area. Particularly in the area of heavy vehicle systems, such as light armored vehicles, little related research has been done, and there exists no commercially available controllable damper suitable for the relatively high force and large displacement requirements of such application. As the first response to these requirements, this thesis describes the design and modeling of an in-house semi-active twin-tube shock absorber with an internal variable solenoid-actuated valve. A full-scale semi-active damper prototype is developed and the shock absorber is tested to produce the required forcing range. The test results are compared with results of the developed mathematical model. To gain a better understanding of the semi-active suspension controlled systems and evaluate the performance of those systems, using perturbation techniques this thesis provides a detailed nonlinear analysis of the semi-active systems and establishes the issue of nonlinearity in on-off semi-active controlled systems. Despite different semi-active control methods and the type of actuators used in a semi-active controlled system, one important practical aspect of all hydro-mechanical computer controlled systems is the response-time. The longest response-time is usually introduced by the actuator -in this case, controllable actuator - in the system. This study investigates the effect of response-time in a semi-active controlled suspension system using semi-active dampers. Numerical simulations and analytical techniques are deployed to investigate the issue. The performance of the system due to the response-time is then analyzed and discussed. Since the introduction of the semi-active control strategy, the challenge was to develop methods to effectively use the capabilities of semi-active devices. In this thesis, two semi-active control strategies are proposed. The first controller to be proposed is a new hybrid semi-active control strategy based on the conventional Rakheja-Sankar (R-S) semi-active control to provide better ride-handling quality for vehicle suspension systems as well as industrial vibration isolators. To demonstrate the effectiveness of this new strategy, the analytical method of averaging and the numerical analysis method are deployed. In addition, a one-degree-of-freedom test bed equipped with a semi-active magnetorheological (MR) damper is developed. The tests are performed using the MATLAB XPC-target to guarantee the real-time implementation of the control algorithm. The second controller is an intelligent fuzzy logic controller system to optimize the suspension performance. The results from this intelligent system are compared with those of several renowned suspension control methods such as Skyhook. It is shown that the proposed controller can enhance concurrently the vehicle handling and ride comfort, while consuming less energy than existing control methodologies. The key goal of this thesis is to employ the existing knowledge of the semi-active systems together with the new ideas to develop a semi-active suspension system. At the same time, development of an experimental simulation system for real-time control of an experimental test bed is considered. To achieve its goals and objectives, this research study combines and utilizes the numerical simulations and analytical methods, as well as lab-based experimental works. The challenge in this research study is to identify practical and industrial problems and develop proper solutions to those problems using viable scientific approaches.