In recent years, many investigators have predicted that with a semiactive suspension it is possible to attain performance gains comparable to those possible with a fully active suspension. In achieving this, the method by which the damper is controlled is one of the crucial factors that ultimately determines the success or failure of a particular semiactive suspension. This study is an investigation into the effectiveness of a number of basic control strategies at controlling vehicle dynamics, particularly vehicle roll. The test vehicle is a Sport Utility Vehicle (SUV), a class of vehicle that regularly sees widely varying vehicle weight (as a result of passengers and load) and can exhibit undesirable levels of vehicle roll. This study includes a suspension system comprised of four controllable magneto-rheological dampers, associated sensors, and controller. There are three distinct phases in this investigation, the first of which is a numerical investigation performed on a four-degree-of-freedom vehicle roll-plane model. The model is subjected to a variety of road and driver induced inputs, and the vehicle response is characterized, with each semiactive control policy. The second phase of this study consists of laboratory testing performed on a Ford Expedition, with the front axle of the vehicle placed on a two-post dynamic rig (tire coupled), and a variety of road inputs applied. The third phase of this testing involves road testing the test vehicle to further evaluate the effectiveness of each of the semiactive control policies at controlling both vehicle comfort (vibration) and stability (roll). In each phase, the semiactive control policies that are investigated are tuned and modified such that the best possible performance is attained. The performance of each of these optimal semiactive systems is then compared. In the first phase of this investigation, two basic skyhook control strategies are investigated and two modified strategies are proposed. Upon numerically investigating the effectiveness of the four control strategies, it is found that the performance achievable with each of the control strategies is heavily dependent on the properties of the controllable damper. The properties of the controllable damper that were particularly important were the upper and lower levels of force that the controllable damper was able to apply. Based on numerical results, the controllable dampers were tuned for each control system. The results indicate that a velocity-based skyhook control policy, in conjunction with force control, is most effective at controlling both road-induced vibration and driver-induced roll. In the second phase of this investigation, the effects of the two skyhook control strategies were again examined. Multiple system inputs including step inputs, chirp inputs, and multi-sine inputs were used, and the results indicate that significant performance gains using the basic skyhook policies are unlikely. The third phase involved road testing the vehicle through specific maneuvers modeling a wide variety of common driving situations. In addition to the two basic skyhook policies, two additional policies augmented with steering wheel position feedback were also examined. It was found that the velocity based skyhook control policy augmented with steering wheel position feedback achieved performance superior to both the stock passive dampers and other control policies tested here. / Ph. D.

This study evaluates the performance of a semiactive magnetorheological primary suspension on a heavy truck application. A set of magnetorheological dampers is designed, fabricated, and characterized. The set of magnetorheological test dampers are implemented on a Volvo VN heavy truck. An embedded controller determines the level of damping to be supplied by the test dampers. The level of damping in each of the controllable magnetorheological dampers is determined according to a skyhook control scheme. Eleven PCB Piezotronics accelerometers are used to measure the acceleration at various points on the truck. The measurement positions include four measurements on the axles of the truck, and four measurements on the frame of the truck. This data is both recorded for post-test analysis and determining the damping level during testing. Q Additionally, three accelerometers measure the roll, heave, and pitch of the truck cab. The performance of the truck equipped with the semiactive magnetorheological suspension is primarily compared to the performance of the truck with the original (stock) passive system. Results from operation with the adjustable dampers fixed in both their on and off states are also given. The performance comparison between the semiactive and the original passive system is performed for two different driving situations. The first comparison between the two suspension types is for a test case where the truck is driven over a speed bump at approximately 6-7 mph. The second comparison is for the test case where the truck is driven at a constant speed along a stretch of straight and level highway at a constant speed of 55 mph. Acceleration data for both of these test cases is analyzed in the time domain (RMS and peak values of acceleration), and in the frequency domain (average peak intensity in different frequency bands). The findings presented here are confined to the specific magnetorheological dampers that were tested on the truck. Little effort was spent on tuning the high and low states of the adjustable dampers. In addition, the controller used was relatively crude, in the sense that it only implemented the on-off skyhook policy. The findings are meant to highlight some of the potential benefits, as well as shortcomings, of the magnetorheological dampers for heavy truck applications. The data for driving the truck over speed bumps indicate that the magnetorheological dampers used in this study with the skyhook control policy have only a small effect on the vehicle body and wheel dynamics, as compared to the passive stock dampers. The highway data shows that magnetorheological dampers and skyhook control policy are effective at reducing the RMS value of the measured acceleration at most measurement points, as compared to the stock dampers. / Master of Science

A new system identification algorithm, multiple autoregressive exogenous (ARX) inputs-based Takagi-Sugeno (TS) fuzzy model, is developed to identify nonlinear behavior of structure-magnetorheological (MR) damper systems. It integrates a set of ARX models, clustering algorithms, and weighted least squares algorithm with a TS fuzzy model. Based on a set of input-output data that is generated from building structures equipped with MR dampers, premise parameters of the ARX-TS fuzzy model are determined by clustering algorithms. Once the premise part is constructed, consequent parameters of the ARX-TS fuzzy model are optimized by the weighted least squares algorithm. To demonstrate the effectiveness of the proposed ARX-TS fuzzy model, it is applied to a three-, an eight-, a twenty-story building structures. It is demonstrated from the numerical simulation that the proposed ARX-TS fuzzy algorithm is effective to identify nonlinear behavior of seismically excited building structures equipped with MR dampers. A new semiactive nonlinear fuzzy control (SNFC) algorithm is developed through integration of multiple Lyapunov-based state feedback gains, a Kalman filter, and a converting algorithm with TS fuzzy interpolation method. First, the nonlinear ARX-TS fuzzy model is decomposed into a set of linear dynamic models that are operated in only a local linear operating region. Based on the decomposed models, multiple Lyapunov-based state feedback controllers are formulated in terms of linear matrix inequalities (LMIs) such that the structure-MR damper system is globally asymptotically stable and the performance on transient responses is guaranteed. Then, the state feedback controllers are integrated with a Kalman filter and a converting algorithm using a TS fuzzy interpolation method to construct semiactive output feedback controllers. To demonstrate the effectiveness of the proposed SNFC algorithm, it is applied to a three-, an eight-, and a twenty-story building structures. It is demonstrated from the numerical simulation that the proposed SNFC algorithm is effective to control responses of seismically excited building structures equipped with MR dampers. In addition, it is shown that the proposed SNFC system is better than a traditional optimal algorithm, H2/linear quadratic Gaussian-based semiactive control strategy.

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.

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.

This study evaluates and provides solutions to the problem of poor subjective feel of seat suspensions that employ magnetorheological (MR) dampers and skyhook control. An Isringhausen seat suspension that had been modified to replace the stock passive damper with a controllable MR damper was used to evaluate the problems and potential solutions. A seat suspension tester was built using materials from 80/20 Incorporated and a hydraulic actuation system from MTS. An HP Dynamic Signal Analyzer was used as the main piece of data acquisition equipment, along with a Pentium PC and National Instruments Data Acquisition card. All of the hardware is installed in a controlled laboratory facility at Virginia Tech's Advanced Vehicle Dynamics Lab. The first task was to analyze the source of the unexpected peak in the acceleration spectrum of the suspended seat. This analysis was accomplished using a combination of pure tone inputs and a Fourier analysis of a simple model of the system. This analysis indicated that the peak is actually three times the resonant frequency of the seat suspension. The analysis also indicates that the frequency components continue at odd multiples of the resonant frequency, however, the third peak is the most noticeable. The third multiple is in the resonant frequency range (4-8 Hz) of the human body, so it was initially blamed for the poor subjective feel of the seat. However, solutions to remove this harmonic were tested without success. The work progressed to a time domain analysis, which eventually led to determining the source of the poor subjective feel. The seat suspension was excited with a variety of inputs. The seat acceleration and damper control current were examined in the time domain to show that the cause of the poor subjective feel is the control signal discontinuities. The control policy was modified to remove the control signal discontinuities and was found to improve the subjective feel of the seat. Finally, several two-degree-of-freedom control policies were implemented and tested. Although the results from this testing are inconclusive, they generated several recommendations for future research. / Master of Science

Truck drivers are exposed to vibrations all day as a part of their work. In addition to repetitive motion injuries the constant vibrations add to the fatigue of the driver which in turn can have safety implications. The goal of this research is to lower the vibrations an occupant of a class 8 semitruck cab sleeper is exposed to by improving the ride quality. Unlike prior research in the area of ride comfort that target the chassis or seat suspension, this work focuses on the cab suspension. The current standard in cab suspensions is comprised of some type of spring and passive damper mechanism. Ride improvements can most easily be accomplished by replacing the stock passive dampers with some type of controllable damper; in this case Magneto-Rheological (MR) dampers. MR dampers can change damping characteristics in real time, while behaving like a passive damper in their OFF state. This means that in case of a failure to the power supply, the dampers still retain their functionality and can provide some level of damping. Additionally, MR dampers can be packaged such that they do not require any redesign of mounting bracketry on the cab or the frame, their use as a retrofitable device. The damper controller is based on the skyhook control policy pioneered by Karnopp et al. in the 1970s. A variation on skyhook control is chosen called no-jerk skyhook control. A controller called Hierarchical SemiActive Control (HSAC) is designed and implemented to allow the no-jerk skyhook controller to adapt to the road conditions. It also incorporates an endstop controller to better handle the limited rattle space of the cab suspension. The development and initial testing of the controller prototype is done in simulation using a model of the cab and its suspension. The model is derived from first principles using bond graph modeling. The controller is implemented in Simulink to ease the transition to hardware testing. The realtime prototype controller is tested on a class 8 semitruck in a lab environment using dSPACE and road input at the rear axles. The laboratory results are veried on the road in a series of road tests on a test truck. The road tests showed a need for HSAC controller. The HSAC is implemented on the test truck in a final prototype system. The test results with this system show signfiicant improvements over the stock passive suspension, especially when dealing with transient excitations. The overall research results presented show that significant ride improvements can be achieved from a semiactive cab suspension. / Ph. D.

In recent years, a flurry of interest has been shown for a relatively old technology called magneto-rheological fluids, or MR fluids. Multiple types of devices have been designed to implement this versatile fluid, including linear dampers, clutches, work-piece fixtures, and polishing machines. The devices have been used in automobiles, washing machines, bicycles, prosthetic limbs, and even smart structures. This thesis focuses on another application of MR dampers, involving super-sport motorcycles. This paper introduces the topics of MR dampers and motorcycle suspensions, and why the two would be a good combination. A detailed history of MR fluids, MR dampers, and motorcycle suspension technologies is given next. After a broad outline of MR dampers and motorcycle suspensions, the method of designing and manufacturing MR dampers is discussed. The damper design for this research is presented in detail, along with the design procedure used to make it. Next, laboratory testing for it is covered, including the test equipment, test procedure, and the laboratory test results. Upon laboratory test completion, the field test setup and procedure are presented. The results of field tests with stock dampers and MR dampers with a variety of control systems is discussed. The MR dampers provided a more stable ride than that of the OEM dampers. By reducing suspension displacement, settling time, and suspension oscillations, the MR dampers were able to reduce suspension geometry instability. Lastly, concluding remarks are made on the research presented. Design flaws are discussed, as well as recommendations for future work in the same area. / Master of Science

This research will compare the transient response characteristics of a four-degree-of-freedom, roll-plane model, representing a class 8 truck, using passive and semiactive dampers. The semiactive damper control policies that are examined include the previously developed policies of on-off skyhook, continuous skyhook, and on-off groundhook control, along with a newly developed method of fuzzy logic semiactive control. The model input will include body forces and torques, as well as transient displacements at the tires. The model outputs include the vehicle body heave and roll displacements, the vertical displacement of the tire (wheel hop) and the vertical acceleration of the vehicle body. For each output, the maximum peak-to-peak and RMS values of the response are examined. The results of the study show that semiactive dampers have minimal effect on improving the vehicle body and tire transients due to forces or torques applied to the body, as compared to passive dampers. For road inputs, however, semiactive dampers are able to provide a more favorable compromise between the body and axle transient dynamics, when compared to passive dampers. The fuzzy logic semiactive control policy that is proposed in this research is better able to balance the body and axle dynamics than the conventional semiactive damping control policies that are investigated. Further research on the application of fuzzy logic semiactive control concepts is suggested, in order to fully investigate the potential of such control schemes for vehicle suspensions. / Master of Science

This analytical study evaluates the response characteristics of a two-degree-of freedom quarter-car model, using passive and semi-active dampers, along with a seven-degree-of-freedom full vehicle model. The behaviors of the semi-actively suspended vehicles have been evaluated using skyhook, groundhook, and hybrid control policies, and compared to the behaviors of the passively-suspended vehicles. The relationship between vibration isolation, suspension deflection, and road-holding is studied for the quarter-car model. Three main performance indices are used as a measure of vibration isolation (which can be seen as a comfort index), suspension travel requirements, and road-holding quality. After performing numerical simulations on a seven-degree-of-freedom full vehicle model in order to confirm the general trends found for the quarter-car model, these three indices are minimized using optimization techniques. The results of this study indicate that the hybrid control policy yields better comfort than a passive suspension, without reducing the road-holding quality or increasing the suspension displacement for typical passenger cars. The results also indicate that for typical passenger cars, the hybrid control policy results in a better compromise between comfort, road-holding and suspension travel requirements than the skyhook and groundhook control policies. Finally, the numerical simulations performed on a seven-degree-of-freedom full vehicle model indicate that the motion of the quarter-car model is not only a good approximation of the heave motion of a full-vehicle model, but also of the pitch and roll motions since both are very similar to the heave motion. / Master of Science