Active suspension control of electric vehicle with in-wheel motors

In-wheel motor (IWM) technology has attracted increasing research interests in recent years due to the numerous advantages it offers. However, the direct attachment of IWMs to the wheels can result in an increase in the vehicle unsprung mass and a significant drop in the suspension ride comfort performance and road holding stability. Other issues such as motor bearing wear motor vibration, air-gap eccentricity and residual unbalanced radial force can adversely influence the motor vibration, passenger comfort and vehicle rollover stability. Active suspension and optimized passive suspension are possible methods deployed to improve the ride comfort and safety of electric vehicles equipped with inwheel motor. The trade-off between ride comfort and handling stability is a major challenge in active suspension design. This thesis investigates the development of novel active suspension systems for successful implementation of IWM technology in electric cars. Towards such aim, several active suspension methods based on robust H∞ control methods are developed to achieve enhanced suspension performance by overcoming the conflicting requirement between ride comfort, suspension deflection and road holding. A novel fault-tolerant H∞ controller based on friction compensation is in the presence of system parameter uncertainties, actuator faults, as well as actuator time delay and system friction is proposed. A friction observer-based Takagi-Sugeno (T-S) fuzzy H∞ controller is developed for active suspension with sprung mass variation and system friction. This method is validated experimentally on a quarter car test rig. The experimental results demonstrate the effectiveness of proposed control methods in improving vehicle ride performance and road holding capability under different road profiles. Quarter car suspension model with suspended shaft-less direct-drive motors has the potential to improve the road holding capability and ride performance. Based on the quarter car suspension with dynamic vibration absorber (DVA) model, a multi-objective parameter optimization for active suspension of IWM mounted electric vehicle based on genetic algorithm (GA) is proposed to suppress the sprung mass vibration, motor vibration, motor bearing wear as well as improving ride comfort, suspension deflection and road holding stability. Then a fault-tolerant fuzzy H∞ control design approach for active suspension of IWM driven electric vehicles in the presence of sprung mass variation, actuator faults and control input constraints is proposed. The T-S fuzzy suspension model is used to cope with the possible sprung mass variation. The output feedback control problem for active suspension system of IWM driven electric vehicles with actuator faults and time delay is further investigated. The suspended motor parameters and vehicle suspension parameters are optimized based on the particle swarm optimization. A robust output feedback H∞ controller is designed to guarantee the system’s asymptotic stability and simultaneously satisfying the performance constraints. The proposed output feedback controller reveals much better performance than previous work when different actuator thrust losses and time delay occurs. The road surface roughness is coupled with in-wheel switched reluctance motor air-gap eccentricity and the unbalanced residual vertical force. Coupling effects between road excitation and in wheel switched reluctance motor (SRM) on electric vehicle ride comfort are also analysed in this thesis. A hybrid control method including output feedback controller and SRM controller are designed to suppress SRM vibration and to prolong the SRM lifespan, while at the same time improving vehicle ride comfort. Then a state feedback H∞ controller combined with SRM controller is designed for in-wheel SRM driven electric vehicle with DVA structure to enhance vehicle and SRM performance. Simulation results demonstrate the effectiveness of DVA structure based active suspension system with proposed control method its ability to significantly improve the road holding capability and ride performance, as well as motor performance

Dynamic impact of ageing dump truck suspension systems on whole-body vibrations in high-impact shovel loading operations

Surface mining operations typically deploy large shovels, with 100+ tons per pass capacity, to load dump trucks in a phenomenon described as high-impact shovel loading operations (HISLO). The HISLO phenomenon causes excessive shock and vibrations in the dump truck assembly resulting in whole body vibration (WBV) exposures to operators. The truck suspension system performance deteriorates with time; therefore their effectiveness in attenuating vibrations reduces. No research has been conducted to study the impact of ageing suspension mechanisms on the magnitudes of WBV in HISLO operations. This study is a pioneering effort to provide fundamental and applied knowledge for understanding the impact of ageing on the magnitudes of WBV exposures. The effects of underlying ageing processes on a suspension performance index are mathematically modeled. The effects of scheduled maintenance and corrective maintenance on improving the performance index (PI) are also modeled. Finally, the proposed mathematical ageing model is linked to the truck operator\u27s exposure to WBVs via a virtual prototype CAT 793D truck model in the MSC ADAMS environment. The effects of suspension system ageing in increasing the WBV levels are examined in the form of both the vertical and horizontal accelerations under HISLO conditions. This study shows that the hydro-pneumatic suspension strut ageing results in deteriorating stiffness-damping parameters. The deteriorating suspension performance (with time) introduces more severe and prolonged WBVs in HISLO operations. The RMS accelerations increase significantly with time (suspension ageing). The vertical RMS accelerations increase to severe magnitudes of over 3.45, 3.75, and 4.0 m/s2 after 3, 5, and 7 years, respectively. These acceleration magnitudes are well beyond the ISO limits for the human body\u27s exposure to WBVs. This pioneering research effort provides a frontier for further research to provide safe and healthy working environments for HISLO operations --Abstract, page iii

Development of Rotary Variable Damping and Stiffness Magnetorheological Dampers and their Applications on Robotic Arms and Seat Suspensions

This thesis successfully expanded the idea of variable damping and stiffness (VSVD) from linear magnetorheological dampers (MR) to rotary magnetorheological dampers; and explored the applications of rotary MR dampers on the robotic arms and seat suspension. The idea of variable damping and stiffness has been proved to be able to reduce vibration to a large degree. Variable damping can reduce the vibration amplitude and variable stiffness can shift the natural frequency of the system from excitation and prevent resonance. Linear MR dampers with the capacity of variable damping and stiffness have been studied by researchers. However, Linear MR dampers usually require larger installation space than rotary MR dampers, and need more expensive MR fluids to fill in their chambers. Furthermore, rotary MR dampers are inherently more suitable than linear MR dampers in rotary motions like braking devices or robot joints. Hence, rotary MR dampers capable of simultaneously varying the damping and stiffness are very attractive to solve angular vibration problems. Out of this motivation, a rotary VSVD MR damper was designed, prototyped, with its feature of variable damping and stiffness verified by experimental property tests in this thesis. Its mathematical model was also built with the parameters identified. The experimental tests indicated that it has a 141.6% damping variation and 618.1% stiffness variation. This damper’s successful development paved the way for the applications of rotary MR dampers with the similar capability of variable damping and stiffness

Theoretical analyses of roll- and pitch-coupled hydro-pneumatic strut suspensions

Vehicle suspension design and dynamics analysis play a key role in enhancement of automotive system performance. Despite extensive developments in actively-controlled suspensions, their commercial applications have been limited due to the associated high cost and weight. Alternative designs in either passive or semi-active suspensions are highly desirable to achieve competitive vehicle performance with relatively lower cost and greater reliability. This dissertation research proposes two hydro-pneumatic suspension strut designs, including a twin-gas-chamber strut, and systematically investigates various concepts in roll- and pitch-coupled suspensions employing hydraulic, pneumatic and hybrid fluidic interconnections between the wheel struts. The proposed strut designs, including single- and twin-gas-chamber struts, offer larger working area and thus lower operating pressure, and integrate damping valves. Nonlinear mathematical models of the strut forces due to various interconnected and unconnected suspension configurations are formulated incorporating fluid compressibility, floating piston dynamics, and variable symmetric and asymmetric damping valves, which clearly show the feedback damping effects of the interconnections between different wheel struts. The properties and dynamic responses of the proposed concepts in roll- and pitch-coupled suspension struts are evaluated in conjunction with in-plane and three-dimensional nonlinear vehicle models. The validity of the vehicle models is demonstrated by comparing their responses with the available measured data. The analyses of the proposed coupled suspensions are performed to derive their bounce-mode, anti-roll, anti-pitch and warp-mode properties, and vehicle dynamic responses to external excitations. These include road roughness, steering and braking, and crosswinds. The results suggest that the fluidically-coupled passive suspension could yield considerable benefits in enhancing vehicle ride and handing performance. Furthermore these offer superior design flexibility. The suspension struts offer a large number of coupling possibilities in the three-dimensions, some of which however would not be feasible, particularly for commercial vehicles where suspension loads may vary considerably. A generalized analytical model for a range of interconnected suspensions is thus developed, and a performance criterion is formulated to assess the feasibility of a particular interconnection in a highly efficient manner. The handling and directional responses of a three-dimensional vehicle model employing X-coupled hydro-pneumatic suspension are evaluated under split-o straight-line braking and braking-in-a-turn maneuvers. The results clearly show that the X-coupled suspension offers enhanced anti-roll and anti-pitch properties while retaining the soft vertical ride and warp properties. Fundamental pitch and vertical dynamics of a road vehicle are also considered to derive a set of essential design rules for suspension design and tuning for realizing desirable pitch performanc

State of the art of control schemes for smart systems featuring magneto-rheological materials

This review presents various control strategies for application systems utilizing smart magneto-rheological fluid (MRF) and magneto-rheological elastomers (MRE). It is well known that both MRF and MRE are actively studied and applied to many practical systems such as vehicle dampers. The mandatory requirements for successful applications of MRF and MRE include several factors: advanced material properties, optimal mechanisms, suitable modeling, and appropriate control schemes. Among these requirements, the use of an appropriate control scheme is a crucial factor since it is the final action stage of the application systems to achieve the desired output responses. There are numerous different control strategies which have been applied to many different application systems of MRF and MRE, summarized in this review. In the literature review, advantages and disadvantages of each control scheme are discussed so that potential researchers can develop more effective strategies to achieve higher control performance of many application systems utilizing magneto-rheological materials

Convolution based real-time control strategy for vehicle active suspension systems

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.A novel real-time control method that minimises linear system vibrations when it is subjected to an arbitrary external excitation is proposed in this study. The work deals with a discrete differential dynamic programming type of problem, in which an external disturbance is controlled over a time horizon by a control force strategy constituted by the well-known convolution approach. The proposed method states that if a control strategy can be established to restore an impulse external disturbance, then the convolution concept can be used to generate an overall control strategy to control the system response when it is subjected to an arbitrary external disturbance. The arbitrary disturbance is divided into impulses and by simply scaling, shifting and summation of the obtained control strategy against the impulse input for each impulse of the arbitrary disturbance, the overall control strategy will be established. Genetic Algorithm was adopted to obtain an optimal control force plan to suppress the system vibrations when it is subjected to a shock disturbance, and then the Convolution concept was used to enable the system response to be controlled in real-time using the obtained control strategy. Numerical tests were carried out on a two-degree of freedom quarter-vehicle active suspension model and the results were compared with results generated using the Linear Quadratic Regulator (LQR) method. The method was also applied to control the vibration of a seven-degree of freedom full-vehicle active suspension model. In addition, the effect of a time delay on the performance of the proposed approach was also studied. To demonstrate the applicability of the proposed method in real-time control, experimental tests were performed on a quarter-vehicle test rig equipped with a pneumatic active suspension. Numerical and experimental results showed the effectiveness of the proposed method in reducing the vehicle vibrations. One of the main contributions of this work besides using the Convolution concept to provide a real time control strategy is the reduction in the number of sensors needed to construct the proposed method as the disturbance amplitude is the only parameter needed to be measured (known). Finally, having achieved what has been proposed above, a generic robust control method is accomplished, which not only can be applied for active suspension systems but also in many other fields

Experimental evaluation of vehicle cabin noise from suspension induced vibrations using transfer path and psychoacoustic analysis techniques

Given the automotive industry\u27s awareness of the importance of the perception of NVH emissions, there is an increased focus on the psychoacoustics, or sound quality, of vehicle cabin noise. The present work aims to qualitatively evaluate and compare automobile cabin noise by measuring the road-induced noise and vibration of a driven and motored vehicle. Evaluation of transmission paths and psychoacoustic analysis of the cabin acoustics are primary objectives. A psychoacoustic analysis using the acoustic pressure measurements taken inside the vehicle cabin was performed using both subjective and objective approaches. Testing also included vibration measurements from several structural positions to evaluate vibroacoustic excitations. Using this noise and vibration data, it was possible to evaluate the transfer path of the excitation energy into the vehicle cabin. Further, an attempt to establish a correlation between the noise and vibration measurements and the psychoacoustic observations was also proven possible with some inherent limitations

Hybrid Electromagnetic Vibration Isolation Systems

Traditionally, dynamic systems are equipped with passive technologies like viscous shock absorbers and rubber vibration isolators to attenuate disturbances. Passive elements are cost effective, simple to manufacture, and have a long life span. However, the dynamic characteristics of passive devices are fixed and tuned for a set of inputs or system conditions. Thus in many applications when variation of input or system conditions is present, sub-optimal performance is realized. The other fundamental flaw associated with passive devices is that they expel the undesired kinetic energy as heat. Recently, the introduction of electromagnetic technologies to the vibration isolation systems has provided researchers with new opportunities for realizing active/semi-active vibration isolation systems with the additional benefit of energy regeneration (in semi-active mode). Electromagnetic vibration isolators are often suffer from a couple of shortcomings that precludes their implementations in many applications. Examples of these short comings include bulky designs, low force density, high energy consumption (in active mode), and fail-safe operation problem. This PhD research aims at developing optimal hybrid-electromagnetic vibration isolation systems to provide active/semi-active and regenerative vibration isolation for various applications. The idea is to overcome the aforementioned shortcomings by integrating electromagnetic actuators, conventional damping technologies, and stiffness elements into single hybrid packages. In this research, for both semi-active and active cases, hybrid electromagnetic solutions are proposed. In the first step of this study, the concept of semi-active hybrid damper is proposed and experimentally tested that is composed of a passive hydraulic and a semi-active electromagnetic components. The hydraulic medium provides a bias and fail-safe damping force while the electromagnetic component adds adaptability and energy regeneration to the hybrid design. Based on the modeling and optimization studies, presented in this work, an extended analysis of the electromagnetic damping component of the hybrid damper is presented which can serve as potent tool for the designers who seek maximizing the adaptability (and regeneration capacity) of the hybrid damper. The experimental results (from the optimized design) show that the damper is able to produce damping coefficients of 1300 and 0-238 Ns/m through the viscous and electromagnetic components, respectively. In particular, the concept of hybrid damping for the application of vehicle suspension system is studied. It is shown that the whole suspension system can be adjusted such that the implementation of the hybrid damper, not only would not add any adverse effects to the main functionally of the suspension, but it would also provide a better dynamics, and enhance the vehicle fuel consumption (by regenerating a portion of wasted vibration energy). In the second step, the hybrid damper concept is extended to an active hybrid electromagnetic vibration isolation systems. To achieve this target, a passive pneumatic spring is fused together with an active electromagnetic actuator in a single hybrid package. The active electromagnetic component maintains a base line stiffness and support for the system, and also provides active vibration for a wide frequency range. The passive pneumatic spring makes the system fail-safe, increases the stiffness and support of the system for larger masses and dead loads, and further guarantees a very low transmissibility at high frequencies. The FEM and experimental results confirmed the high force density of the proposed electromagnetic component, comparing to a voice coil of similar size. In the proposed design, with a diameter of ~125 mm and a height of ~60 mm, a force variation of ~318 N is obtained for the currents of I=±2 A. Furthermore, it is demonstrated that the proposed actuator has a small time constant (ratio of inductance to resistance for the coils) of less than 5.2 ms, with negligible eddy current effect, making the vibration isolator suitable for wide bandwidth applications. According to the results, the active controllers are able to enhance the performance of the passive elements by up to 80% and 95% in terms of acceleration and force transmissibilities, respectively

Dual Purpose Tunable Vibration Isolator Energy Harvester: Design, Fabrication, Modeling and Characterization

This dissertation is focused on design, fabrication, characterization, and modeling of a unique dual purpose vibration isolation energy harvesting system. The purpose of the system is to, simultaneously, attenuate unwanted vibrations and scavenge kinetic energy available in these vibrations. This study includes theoretical modeling and experimental work to fully characterize and understand the dynamic behavior of the fabricated dual purpose system. In the theoretical study, both numerical (Runge-Kutta) and analytical (Harmonic Balance Method, HBM) methods are used to obtain the dynamic behavior of the system. The system features a combination of mechanical and electromagnetic components to facilitate its dual functionality. The system consists of a magnetic spring, mechanical flat spring, and dampers. The combination of negative stiffness of the magnetic spring with positive stiffness of the mechanical spring results in lowering the cut off frequency of the system. Lowering the cut off frequency improves the device’s ability to operate in a wider range of frequencies. Results from dynamic measurements and model simulation confirm the ability of the device to function in both vibration isolation and energy harvesting modes simultaneously. The dual-purpose device is able to attenuate vibrations higher than 12.5 [Hz]. The device also produces 26.8 [mW] output power at 1g [m/s2] and 9.75 [Hz]. Performance metrics of the device including displacement transmissibility and energy conversion efficiency are formulated. Results show that for low acceleration levels, lower damping values are desirable and yield higher energy conversion efficiencies and improved vibration isolation. At higher acceleration, there is a trade-off where lower damping values worsen vibration isolation but yield higher conversion efficiencies

Modelling, testing and analysis of a regenerative hydraulic shock absorber system

Recoverable energy in vehicle suspension systems has attracted intensive attention in recent years for the improvement of vibration suppression performance and the reduction of energy dissipation. Various design concepts and structures of regenerative suspensions have been presented and investigated to recover the energy of linear motion and vibration between the vehicle body and chassis from road disturbances. These studies concentrate on the energy conversion from kinetic energy to electricity. Although a large number of concepts and models have been proposed and evaluated to regenerate power for reuse, the previous simulation works have used significantly simplified models without considering parameter uncertainties and system losses. In addition, experimental works are too simple to support for modelling optimisation. To advance the technology, a regenerative hydraulic shock absorber is investigated rigorously by examining the system at various developing stages including modelling all hydraulic, mechanical, and electromagnetic processes, simulating its behaviours, identifying its uncertain parameters/variables, fabricating a prototype of a commonly used shock absorber, testing its desirable performance and evaluating its on-road usability, which has given an accurate understanding of dynamic behaviours and power regeneration of a regenerative hydraulic shock absorber system. Based on the configuration of the prototype, a comprehensive mathematical model is developed for the regenerative hydraulic shock absorber system. The various losses and nonlinearity have been taken into account in modelling hydraulic, mechanical, and electromagnetic processes, which allow more detailed influences and agreeable predictions with the experimental work to be obtained. The introduction of the gas-charged hydraulic accumulator into the system has been explored in both modelling and testing to provide power smoothing in an attempt to give a more stable recoverable power. Model parameter identifications and refinements based on online data are systemically investigated. It has found that the pressures, rotation speeds and electrical outputs, which are readily available in the system, are sufficient to determine and refine uncertain model parameters such as the voltage constant coefficient, torque constant coefficient, generator internal resistance and rotational friction torque using a common least square method. The developed experimental rig and measurement systems for the study of regenerative hydraulic shock absorbers are designed and built. The variations in motor pressure and shaft speed under different excitations are evaluated, and also voltage output and recoverable power at different electrical loads are investigated. Additionally, the experimental work is not only used to validate the predicted results comprehensively, but also to offer a practical evaluation method for the system under various operating conditions. In particular, the system using piston-rod dimensions of 50-30mm achieves recoverable power of 260W with an efficiency of around 40% under sinusoidal excitation of 1Hz frequency and 25mm amplitude. Additionally, control strategies and their realisation on a general purpose PC computer are developed based on constant voltage, current and resistance schemes to carry out the investigation of the system performances, which allows it to be fully evaluated upon the compromise between the damping behaviour and power regeneration performance for different road conditions. Furthermore, the simulation of the entire system and parameter computations are all realised on the Matlab platform, which provides sufficient flexibility to take into account more influence factors for accurate and detailed analysis and thus can be an effective mathematical tool for further development research in this direction such as the optimisation of the structures, control strategies and system integrations