Active Suspension Research Articles

Velocity and load dependent dynamic shock absorber friction at stationary conditions

When it comes to vehicle vertical dynamics, the characteristics of shock absorbers are of high importance. With the increasing use of active suspension systems, it becomes possible to adapt the hydraulic damping force to the road event, while the friction force is not controllable. As a result, friction becomes more relevant and can negatively affect passenger ride comfort. In many mechanical applications, it is observed that friction in lubricated sliding conditions is velocity and load dependent. In contrast, shock absorber friction, and therefore suspension friction, is commonly considered as quasi-static, i.e. characterised by a constant potential. Since the shock absorber is predominantly in motion over a wide velocity range, it is necessary to improve the understanding of friction characteristics especially in the dynamic domain. In this study, modified valve-free shock absorbers are presented that allow the observation of dynamic friction properties experimentally. As not covered by previous studies, the effect of side force (load) as a main parameter to increase friction is investigated. It is observed that its effect varies significantly with velocity and alters the stationary friction-velocity curve, also known as the Stribeck curve. In addition, the shape of the Stribeck curve depends strongly on the shock absorber's oil volume. These novel results emphasise a substantial, interdependent influence of load and velocity on the (elasto-)hydrodynamic properties of the dynamic shock absorber friction force, which was not identified in the literature. The dynamic friction force exceeds the quasi-static friction force multiple times, and also exceeds the hydraulic damping force for considerable side forces in the lower velocity range up to 60 mm/s. Consequently, the total shock absorber force under presence of side force is determined. The findings can be used to improve active suspension control or to improve vehicle simulation by enabling the parametrisation of dynamic shock absorber friction models.

Aliasing Suppression Method for a Three-Phase Grid-Connected Photovoltaic Inverter Based on Multi-Sampling and Mean Filtering

In order to reduce the sampling delay and improve bandwidth, sability margin, and the robustness of the active damping in LCL-filtered grid-connected inverters, real-time sampling provides a convenient method. However, aliasing is easily introduced in the control loop because of high-frequency switching harmonics, resulting in a rise in low-order harmonics. To address the challenge of aliasing under real-time sampling, a new method based on multisampling and mean filtering is proposed by combining the proposed harmonic detection and control methods in this paper. This method works by sampling and controlling the fundamental current and selective subharmonic currents separately. The fundamental current control loop without any additional filters maintains real-time sampling, while multisampling and mean filters are applied to the harmonic current control loop. The proposed control method can not only improve the dynamic response performance and control stability of the system but also effectively suppress the selective low-order current harmonics and the aliasing of sampling. Finally, the correctness of the proposed sampling scheme and control strategy is verified by the simulation based on R2018b, MathWorks, Natick, MA, USA and an experimental prototype of a three-phase grid-connected photovoltaic inverter rated at 230 V/50 Hz/40 kW.

Nursing Instructors’ and Students’ Experiences of Transition from Face-to-Face Education to Virtual Education during the Coronavirus Disease 2019 Pandemic

Introduction. The coronavirus disease 2019 (COVID-19) pandemic necessitated the suspension of most educational activities and a shift from face-to-face (FTF) education to virtual education (VE). These changes were associated with new educational experiences for both instructors and students. This study aimed to explore nursing instructors’ and students’ experiences of VE during the COVID-19 pandemic. Method. This descriptive qualitative study was carried out in 2021. Participants were 21 bachelor’s, master’s, and Ph.D. nursing students and six nursing instructors purposively selected from the Faculty of Nursing and Midwifery of Tehran University of Medical Sciences, Tehran, Iran. Data were gathered through FTF or online in-depth semistructured interviews and were analyzed through conventional qualitative content analysis as proposed by Graneheim and Lundman (2004). Results. Eight subthemes and three main themes were developed during data analysis. The main themes and subthemes were VE as a double-edged sword (VE as a threat, VE as an opportunity, and necessity to improve VE), weaknesses in clinical education (reduced quality of clinical education and necessity to compensate for students’ retarded clinical learning), and reduced reliability of virtual student evaluation (cheating as a problem of virtual evaluation, stresses and tensions of virtual evaluation, and necessity to use new strategies in virtual evaluation). Conclusion. Despite the different shortcomings and challenges of VE during the COVID-19 pandemic, educational experiences gained in this period can be used to improve the quality of nursing VE in future epidemics and pandemics.

Explicit solution to the nonlinear geometry of double wishbone suspension by decoupling steering and wheel jumping DOF

The suspension system is vital to vehicle performance because it undertakes most of the interactions between wheels and the vehicle body. Due to the significant geometric nonlinearity, there is still a gap of suitable suspension models that are both accurate and computationally efficient. To solve the problem, this paper proposes an explicit solution to the nonlinear geometry of double wishbone suspension by decoupling steering and wheel jumping degrees of freedom (DOF). By discarding the small displacement assumption in the derivation process, the new model gets rid of repeated numerical iterations, resulting in substantial enhancement in computational efficiency. Furthermore, it is noticed in the comparative study that the proposed model can achieve the same level of accuracy as Adams. Benefiting from high computational efficiency and accuracy, the decoupling model presented is successfully used in the optimal design of a double wishbone suspension for smaller variation ranges of wheel alignment parameters. It is anticipated that the research will make significant contribution to fast dimension design of suspension geometry and real-time control of active variable geometry suspensions.

Proportional-retarded control of a quasi-zero-stiffness vibration isolator

This paper explores the control design and performance analysis of an active quasi-zero-stiffness vibration isolator utilizing the proportional-retarded (PR) control architecture. The PR architecture replaces the conventional “derivative” term in the proportional-derivative (or displacement-velocity) controller with the novel “retarded (time-delayed)” term, which is a new and effective way of active vibration suppression. Comprehensive gain-delay conjoint regulation strategies are developed for the strengthened isolation performance. For impact excitations, a complete stability analysis is conducted near the equilibrium position. Furthermore, a parameterized dominant pole placement algorithm is proposed to optimize the transient response of the PR-actuated isolator. Focusing on the rectangular pulse and long-duration step impacts, the algorithm adjusts the dominant poles to optimize the transient performance metrics, including the maximum displacement overshoot, steady-state displacement overshoot, and settling time. Regarding harmonic excitations, the delay-coupled effect is scrutinized for better low-frequency isolation performance, including the resonance frequency, nonlinear steady-state amplitude, multiple steady-state bands and nonlinearity elimination, equivalent active damping and stiffness, and absolute displacement transmissibility. In the case of random excitations, we demonstrate the superiority of the PR structure over the passive system.

Research on variable universe fuzzy PID control for semi-active suspension with CDC dampers based on dynamic adjustment functions

The vehicle suspension system is a complex system with multiple variables, nonlinearity and time-varying characteristics, and the traditional variable universe fuzzy PID control algorithm has the problems of over-reliance on expert experience and non-adaptive adjustment of the contracting-expanding factor parameters, which make it difficult to achieve a better control effect. In this paper, the system error e(t) and its change rate ec(t) are introduced into the contracting-expanding factor as dynamic parameters to realize the adaptive adjustment of the contracting-expanding factor parameters, and propose a variable universe fuzzy PID control based on dynamic adjustment functions (VUFP-DAF), which uses the real-time contracting-expanding factor to realize the adaptive adjustment of the fuzzy universe, so as to improve the ride comfort of vehicles. The research results show that the proposed VUFP-DAF has strong adaptability and can effectively improve the ride comfort and handling stability of vehicles under different speeds and road excitations, providing a certain technical basis for the development of the semi-active suspension system.

Study on Modeling and Control for a Novel Active Suspension

Study on Modeling and Control for a Novel Active Suspension

Relative threshold event-triggered prescribed performance control for vehicle active suspension systems with uncertainty

This paper proposes a novel control strategy to solve the tracking problem for uncertain vehicle active suspension systems (VASS). Under the proposed control framework, the overall VASS is divided into two subsystems owing to its particular structure: (1) for the first subsystem, to ensure the important state variable within the given restrictive conditions all the time, a novel prescribed performance control(PPC)-based intermediate controller is first designed; furthermore, a new relative threshold event-triggered controller is proposed based on the event-triggered control theory; Moreover, because the internal and external disturbances are inevitable in actual applications, system uncertainties are also considered. (2) for the second subsystem, which is regarded as zero dynamics of overall VASS, the corresponding zero dynamic stability analysis is presented; finally, the resulting closed-loop system is ensured to be stable in the sense of uniform ultimate boundedness. The effectiveness of the proposed approach is illustrated by simulation results.

LQR-Based Suspension for Heavy Vehicles Considering the Time-Varying Characteristics of Vehicle–Road Interaction

The rapidly increasing demand for heavy vehicles in the transportation sector has led to more severe road damage and significantly higher road maintenance costs. Investigation of active suspension system incorporating vehicle–road interaction (VRI) can provide effective means to reduce the road damage and improve the ride comfort of vehicles. In this paper, an active vehicle suspension controller based on the strongly stable and robust linear–quadratic regulator (LQR) principle is developed for the time-varying VRI system. The coupled system is modeled by a quarter-car traveling on the road modeled by an Euler–Bernoulli beam resting on a viscoelastic foundation. Two types of road irregularities, deterministic sine wave and random, are considered in the numerical studies. A time-frozen technique, by which the linear time-varying system is converted to a time sequence of time-invariant systems, is applied to solve for the coupled responses. Three variables, the dynamic tire load, vehicle body acceleration, and suspension relative displacement, are used to assess the effectiveness of the LQR-based controller in comparison to the passive suspension system. The performance of the active control is investigated for different vehicle speeds, vehicle loads, and road profiles. Numerical studies show that the controller can effectively reduce the road damage and improve the ride comfort, with a slight increase in the suspension relative displacement. This work lays a useful foundation in the problem formulation and system parameter influences for future vehicle suspension design and road damage mitigation including VRI.

Modeling and Simulation of Active Half-vehicle Suspension Based on a New Output-feedback H∞ Controller

Modeling and Simulation of Active Half-vehicle Suspension Based on a New Output-feedback H∞ Controller

Optimal FLC-Sugeno Controller based on PSO for an Active Damping System

In this paper, a method for the design of an optimal Sugeno model (FLC-Sugeno) fuzzy logic controller for the active suspension system of quarter-vehicle models is presented. The parameters of the FLC-Sugeno controller are optimally searched, using the Particle Swarm Optimization (PSO) algorithm. The 16 optimized parameters include 3 parameters for adjusting the domain of the input state variables and control variables at the controller’s output, 4 fuzzy set adjustment numbers of the linguistic variables, and 9 parameters as the fuzzy rule weights of the rule system control. To compare and evaluate the effectiveness of the optimal FLC-Sugeno controller, an optimal PID controller using PSO is also implemented. Simulation results of the active damping system with the controllers when affected by the same type and standard road surface excitation show that the FLC-Sugeno controller is optimal for the quick ending of the oscillations of vehicle body displacement. The result shows that the proposed controlling scheme can be extended and applied to more complex active damping system models.

Enhancing Road Holding and Vehicle Comfort for an Active Suspension System utilizing Model Predictive Control and Deep Learning

Active Suspension Systems (ASS) with control are gaining traction as researchers strive for optimal system performance. They are significant in diverse commercial vehicle applications, catering to user demands. This study employs the advanced Model Predictive Control (MPC) technique to enhance the smoothness and safety of a half-car model. The simulation results showed the prowess of MPC controllers under varied control force signal constraints, demonstrating superiority in curtailing vehicle chassis rotation angle and speed by up to 46.93% and 43.34%, respectively. The controller was compared with an artificial neural network controller utilizing only two state signals of the system, trained from MPC data, demonstrating high accuracy with R2 reaching 0.97024 and mean squared error at 7.3557×10-5. This study contributes to the refinement of ASS by focusing on practical implementation and performance enhancement.

Vision based road profile estimation for preview-controlled vehicle suspension systems

In this paper, a vision-based road profile estimation method was studied for the control of semi-active and active suspension systems. For the purpose, a monocular camera was used to collect data from the road tests to develop a logic to convert the camera measurements into the road profile data. For the generation of the road profile, alignment of the different sets of camera measurements and their coherence were expressed. Importance of the sensor and process noise removal were shown in recognition of the high frequency content of the road profile, which was a particular interest of the study. Additionally, a density-based clustering algorithm was taken into account to cluster the measured points vertically, to remove the process and sensor noise. The density-based clustering method reduced the noises and allowed detection of the high and low frequency contents of the road.

Research of time lag characteristics of Pilot-operated Solenoid Valve Damper based on multi-physics field

The development of semi-active suspensions has introduced Pilot-operated Solenoid Valve Dampers (PSVD) that can adjust damping characteristics for different road conditions while considering stability and comfort. However, the PSVD’s additional control system and valve-controlled components make it challenging to avoid time lag in the response of the damping force when the control current signal is switched. This time lag characteristic significantly impacts the performance of the control system, making it difficult to achieve optimal dynamic performance and potentially compromising the safety of drivers and passengers. As a result, understanding and representing the PSVD time lag characteristics and investigating their influence have become important research areas in the field of semi-active suspension. This article begins by explaining the mechanism behind the generation of PSVD time lag characteristics. It analyzes the structure and operating principle of the PSVD, identifying two main types of time lag: electromagnetic time lag and inertial time lag. To address the limitations of existing simulation models, the study combines parameterization and finite element simulation to create a multi-physics field time lag characteristics kinetic representation model of the PSVD, incorporating the electric, magnetic, mechanical, and fluid aspects. To validate the accuracy of the time lag characteristics simulation model, tests on the velocity and time lag characteristics of the PSVD are conducted. The simulation results are compared to the test results, demonstrating that the maximum error of the lag time meets the engineering confidence requirement. This confirms the feasibility of establishing a simulation model for the PSVD time lag characteristics. Finally, we analyze the PSVD total lag time under different working conditions using the simulation model. It explores the relationship between the PSVD total lag time and the lag time of each component, proposes a lag time decomposition relationship, and investigates the crucial influencing factors on the lag time.

Rubber-Tracked Forwarders—Productivity and Cost Efficiency Potentials

The extraction of timber is expensive, energy intensive, and potentially damaging to the forest soil. Machine development aims to mitigate risks for environmental impact and decrease energy consumption while maintaining or increasing cost efficiency. The development of rubber-tracked forwarders has gained renewed interest, not least due to climate change leading to unreliable weather in combination with low tolerance for soil damage. The increased cost of rubber tracks compared to wheels is believed to be compensated by higher driving speed enabled by semi-active suspension. Thus, the aim of this study was to theoretically investigate how the productivity and cost efficiency of rubber-tracked forwarders are affected by variations in driving speed and machine costs. The calculations were made with fixed stand parameters, to evaluate performance in well-defined working conditions, and with parameters from 2500 final felling stands in central Sweden, to evaluate performance in varied working conditions. Scenarios were compared to a baseline corresponding to mid-sized wheeled forwarders. The results show higher productivity with the increased driving speed enabled by rubber tracks and suspension at all extraction distances, with larger differences at long extraction distances. Assuming a 15% higher machine price for the rubber-tracked forwarder and a variable cost increase proportional to speed increase, extraction costs break even with the baseline at 400 m and 700 m extraction distance for moderate and fast driving speed, respectively. Furthermore, a rubber-tracked forwarder is likely to enable access to a larger part of the harvest area during longer seasons. For the studied set of stands, the year-round accessible volumes are estimated to increase from 9% to 92% with a rubber-tracked forwarder. With rubber tracks instead of wheels, good accessibility has the potential to be combined with low soil impact and cost efficiency in a favourable way for both industry and ecosystem.

Streamwise dispersion of soluble matter in solvent flowing through a tube

For the dispersion of soluble matter in solvent flowing through a tube as investigated originally by G.I. Taylor, a streamwise dispersion theory is developed from a Lagrangian perspective for the whole process with multi-scale effects. By means of a convected coordinate system to decouple convection from diffusion, a diffusion-type governing equation is presented to reflect superposable diffusion processes with a multi-scale time-dependent anisotropic diffusivity tensor. A short-time benchmark, complementing the existing Taylor–Aris solution, is obtained to reveal novel statistical and physical features of mean concentration for an initial phase with isotropic molecular diffusion. For long times, effective streamwise diffusion prevails asymptotically corresponding to the overall enhanced diffusion in Taylor's classical theory. By inverse integral expansions of local concentration moments, a general streamwise dispersion model is devised to match the short- and long-time asymptotic solutions. Analytical solutions are provided for most typical cases of point and area sources in a Poiseuille tube flow, predicting persistent long tails and skewed platforms. The theoretical findings are substantiated through Monte Carlo simulations, from the initial release to the Taylor dispersion regime. Asymmetries of concentration distribution in a circular tube are certified as originated from (a) initial non-uniformity, (b) unidirectional flow convection, and (c) non-penetration boundary effect. Peculiar peaks in the concentration cloud, enhanced streamwise dispersivity and asymmetric collective phenomena of concentration distributions are illustrated heuristically and characterised to depict the non-equilibrium dispersion. The streamwise perspective could advance our understanding of macro-transport processes of both passive solutes and active suspensions.

Online optimal tuning of fuzzy PID controller using grey wolf optimizer for quarter car semi-active suspension system

In order to reduce vibration and increase ride comfort, this article utilizes a system of quarter-car suspension integrated with a Fuzzy PID controller. To build and improve the Fuzzy PID controller for the semi-active suspension system used in quarter cars, using a novel meta-heuristic technique known as Grey Wolf Optimizer (GWO). Here the magnetorheological damper (MR) fluid with the Fuzzy PID controller was examined to optimize using the GWO algorithm. With the GWO technique and the integral of time absolute error (IAE) as a fitness function, the three gain parameters of the Fuzzy PID controller – Kp, Ki, and Kd– have been optimally set. The suggested approach has additional advantages for the optimization of functions with three variables, including simplicity in implementation, quick convergence traits, and superior computational capabilities. This work is significant, to the best of the author’s knowledge there is no optimization method using GWO to online tune a Fuzzy PID controller for a semi-active suspension system. The optimal output parameters of the controller can be updated online in real-time by GWO. The performance of the proposed controller was examined by assessing the root mean square (RMS) values and peak-to-peak (PTP) values of body displacement and body acceleration under various road profiles. To ensure that the intelligent controller was of the highest caliber, an online test rig was constructed. Results from simulations and online experiments demonstrated that the Fuzzy GWO PID controller significantly improved ride comfort under a variety of road conditions when compared to the Fuzzy PID controller and passive suspension system.

Current Sensor-Free Output-Feedback Voltage Control for DC/DC Converters via Critical Damping Injection Technique for Converter-Fed Servo System Applications

This study proposes an observer-based multi-loop output-feedback system that regulates the output DC-link voltage of DC/DC converters to the desired value to lower the system model dependence level. There are a few features: (a) the outer loop injecting the nonlinear active damping to ensure the critically damped output voltage response, (b) a model-independent output voltage derivative observer facilitates the inner loop and eliminates the need for complex matrix calculations for tuning the estimation performance, and (c) the use of a pole-zero cancellation acceleration error stabilizer for the inner loop helps maintain the targeted closed-loop performance. The experimental study adopts a 420 W brushless DC motor dynamo system as the load for the prototype 600 W bi-directional converter controlled using the proposed solution.

Reluctance-Based Modular Active Damper for Chatter Suppression in Boring Bars With Different Overhangs

Reluctance-Based Modular Active Damper for Chatter Suppression in Boring Bars With Different Overhangs

ANFIS-based FOPID controller to enhanced stability of cascaded converter for electric vehicle (EV) charger

In an electric vehicle (EV) charger system, a two-stage conversion process is integrated and cascaded with a voltage source converter (VSC) and a Dual active bridge converter (DAB). These impedances VSC outputs impedance (ZoutVSC(s)) and DAB have input impedance (ZinDAB(s)) interact, leading to voltage fluctuation and power loss. To address the cascaded converter’s impedance interaction, the modified controller that combines an adaptive Neuro-fuzzy inference system (ANFIS) based fractional order proportional integral derivative (FOPID) controller is used with effective active damping (AD). The modified controller (ANFIS + FOPID + AD) uses ANFIS’s skills to capture and predict the system’s nonlinear behaviour, using its trained data to guide the FOPID’s parameter. The presence of AD ensures the sorting out of impedance interaction problems. Compared to the PID controller, the FOPID controller includes two more degrees of freedom and offers superior adaptability and performance. The effectiveness of the modified controller is tested via frequency response analysis and time domain simulations. Time domain simulations underscore the advantage of the modified controller (ANFIS + FOPID + AD), revealing a remarkable 30% settling time and a 25% overshoot compared to the (FOPID + AD) controller. It is better regarding flexibility, faster response time, and improved system stability. The system performance has been validated and compared by simulation process and HIL technique OPAL RT OP44512.