Seat Suspension Research Articles

Theoretical Modeling and Vibration Isolation Performance Analysis of a Seat Suspension System Based on a Negative Stiffness Structure

In this study, to improve the vibration isolation performance of a cab seat and the ride comfort of the driver, we propose a mathematical model for a seat suspension system of a construction machinery cab based on a negative stiffness structure (NSS). First, a static analysis of a seat suspension system is conducted and the different parameters and their influences on the dynamic stiffness are discussed. Thereby, the ideal configuration parameter range of the suspension system is obtained. Moreover, the nonlinear dynamic model of the designed seat suspension system is established. The frequency response and the stability are analyzed by using the HBM method and numerical simulation. The vibration transmissibility characteristics and vibration suppression effects of the seat suspension system are presented in detail. The results show that, as compared with a quasi-zero-stiffness system, the QZS-IE system has higher vibration suppression advantages under large excitation and small damping, as well as lower transmissibility and a wider vibration isolation frequency range. In addition, an inerter element with a larger mass ratio and relatively shorter distance ratio is better for vibration isolation performance of the QZS-IE system in a practical engineering application. The results of this study provide a scientific basis for the design and improvement of a seat suspension system.

Event-triggered H∞ control for active seat suspension systems with state delay

In this paper, the event-triggered control issue for active seat suspension systems is investigated, which considers the problem of the signal collection and control input in discrete time. An active seat suspension system, a discrete-time event-triggered scheme, and an [Formula: see text] controller are designed at first. Some Lyapunov functions are chosen so that the stability criteria of the considered system are established and the event-triggered scheme and [Formula: see text] controller are obtained. The event-triggered scheme can reduce the workload of data transmission. Both simulation and experimental tests illustrate the effectiveness and advantages of the proposed control approach to improve driving comfort and reduce data transmission compared with the uncontrolled seat suspension system.

Robustness control for nonlinear systems based on homogeneous prescribed sliding mode control

This paper presents a new homogeneous control using dual sliding mode control, and robustness control using linear matrix inequality (LMI) constraints. The controller is applied for the severe disturbance. A sliding surface function, which relates to an exponential function and itself t-norm, is applied to save the energy consumption of the control system. The constraints related LMI are proposed with the matrices and vectors of the systems following the chosen matrices in control the energy for control. Solution of the constraints is also presented with new approach to save the time of calculation. In addition, the proof for the proposed controller is also presented by using the candidate Lyapunov function. In the input control function, the t-norm type is embedded to improve its performance in control disturbance. Besides of the t-norm, the modified sliding surface in the input control is also improve the energy for controlling. The combination of these robustness control elements would bring a new view for the design of control. The advantages of the controller are demonstrated via computer simulation for a seat suspension system. A magneto-rheological fluid seat suspension with its random disturbances is used. To prove the flexibility of the controller, the proposed approach is compared with an existing controller. The compared control has the same structure as shown in the proposed model. However, its design has a disadvantage in control the severe disturbance. The comparison between two controls is a clear view of distinct improvement. The results of simulations show that the controller provides better performance and stability of the system. The stability is also analyzed through the variation of the input control and power spectral density related energy consumption.

Modeling, design and investigation of seat suspension based on negative stiffness structure to improve the vibration environment for helicopter pilots

The vibration transmitted to helicopter aircrew is the main risk factor for their health. In this paper, a seat suspension based on a negative stiffness structure is proposed to improve the vibration environment for the aircrew. The main advantage of the proposed seat suspension is mitigation of vibration transmitted to occupant in the same time keeping the system payload capacity. Hereafter deriving the dynamic model of the proposed system, the occupant model is attached to achieve an integrated occupant-seat-suspension model. Next, the design procedure of suspension parameters is presented to reduce the vibration transmission. In order to reach realistic results, the simulations are performed using the measured data on Bell-412 helicopter cabin floor. Then, the level of vibrations transmitted to seat and pilot body parts are evaluated using ISO-2631 and common criteria. The results show the performance of system based on negative stiffness structure is good in terms of vibration reduction so that root mean square and vibration dose value of vertical vibration for pilot’s body parts are mitigated about 40% in comparison with cabin floor vibration. Also, according to ISO-2631, comfort level is upgraded from uncomfortable to a little uncomfortable which represents promotion of ride quality and improvement of vibration environment for the pilot. Furthermore, the results indicate that no frequency modulation happens in the vibration transfer path from the cabin floor to the pilot’s head.

A nonlinear seat suspension with high-static low-dynamic stiffness based on negative stiffness structure for helicopter

One of the most important issues for the helicopter pilots is the health risk due to the vibration transmitted to the pilot through the seat. In this article, a seat suspension based on negative stiffness structure is presented to decrease the vibration transmitted to the pilot in both vertical and lateral directions without losing the loading capacity of the system. Here, an integrated model of the suspension–cushion–occupant is derived. To generalize the results of system analysis and its usability in other applications, the impact of parameters on the system performance is studied in dimensionless form. Despite coupling between the lateral and vertical directions, the design parameters of the seat suspension are determined in such a way that the system responds simultaneously as a negative stiffness structure in both directions. The system efficiency in vibration damping is assessed by seat effective amplitude transmissibility and transmissibility criteria. In addition, the whole body vibration and impact of the vibration on the pilot body are evaluated using ISO-2631. To verify the system efficiency in more realistic situation, the simulations are performed using the measured vibration data of a Bell-412 helicopter. The results indicate that the vibration amplitude is decreased by about 45% and 48% in the lateral and vertical directions, respectively. The frequency spectrum comparison of the seat and cabin floor reveals 80% reduction of amplitude in fundamental frequency in the vertical direction, whereas it is about 93% in the lateral direction. Furthermore, the level of pilot’s comfort and perception is improved that demonstrates better riding quality and reduced vibration environment.

The Wavelet as the Evaluation Tool of Vehicles’ Seat Suspension System

The Wavelet as the Evaluation Tool of Vehicles’ Seat Suspension System

Friction observer-based hybrid controller for a seat suspension with semi-active electromagnetic damper

This paper proposes a hybrid controller for a seat suspension equipped with an advanced electromagnetic damper (EMD) system to meet the requirement with vibration isolation and energy saving. The friction of seat suspension has considerable influence on the system dynamic. Applying a constant model to describe the friction is unreliable due to the long term wear and tear. Therefore, an observer is designed to estimate seat suspension friction, and it is used to compensate for the frictional influence in a H∞ controller. The friction observer applies the acceleration, relative displacement and circuit current, which are measurable in engineering. Then, a hybrid controller is further proposed, in which the low-frequency vibration is controlled with the friction observer-based H∞ controller, and the system will switch to passive state with low damping at high frequency based on the dominant frequency of the vibration. In order to validate the effectiveness of the proposed friction observer, the Bouc-Wen friction model is selected to describe actual seat suspension friction, and it is compared with the estimated friction by the observer. Experimental results show that the friction observer has similar performance and less computational complexity compared with the Bouc-Wen friction model. The effectiveness of the proposed hybrid controller is validated on a six-degree of freedom vibration platform with the bump and random excitation. This friction observer-based hybrid controller is helpful for the engineering application as it applies practically measurable variables as feedback and considers the performance of the semi-active device in reality.

An Electromagnetic Variable Inertance and Damping Seat Suspension With Controllable Circuits

This article proposes a novel semiactive electromagnetic device with the capability of variable inertance and damping (VIVD) and an energy storage priority control (ESPC) strategy for vibration reduction of vehicle seat suspensions. The VIVD device can control its inertance and damping by adjusting resistances in a variable admittance (VA) circuit different from the traditional mechanical damper. The circuit and mechanical dynamics model of the VIVD seat suspension is analyzed and verified with tests, and the energy storage characteristic and controllability of the VIVD device are explored. Also, the frequency response characteristics of the VIVD device are derived from the admittance characteristics of the VA circuit. For the semiactive VIVD seat suspension, an H∞ controller is designed to obtain the desired control force. An ESPC strategy is proposed to make the electromagnetic force of the VIVD device track the desired control force. The test results show that the VIVD seat suspension can successfully suppress the seat's vibration, which is better than the traditional variable damping seat suspension performance. Under the random excitation, the root means square acceleration of the VIVD seat is reduced by 32.99% compared with a passive seat. This new semiactive VIVD device shows great potential in engineering applications.

Modeling and Parameter Identification of MR Damper considering Excitation Characteristics and Current

Smart structures such as damping adjustable dampers made of magnetorheological (MR) fluid can be used to attenuate vibration transmission in vehicle seat suspension. The main research content of this paper is the nonlinearity and hysteresis characteristics of the MR damper. A hysteretic model considering both excitation characteristics and input current is proposed to fit the damper force-velocity curve for the MR damper under different conditions. Multifactor sensitivity analysis based on the neural network method is used to obtain importance parameters of the hyperbolic tangent model. In order to demonstrate the fitting precision of the different models, the shuffled frog-leaping algorithm (SFLA) is employed to identify the parameters of MR damper models. The research results indicate that the modified model can not only describe the nonlinear hysteretic behavior of the MR damper more accurately in fixed conditions, compared with the original model, but also meet the fitting precision under a wide range of magnitudes of control current and excitation conditions (frequency and amplitude). The method of parameter sensitivity analysis and identification can also be used to modify other nonlinear dynamic models.

Modelling and simulation of active and passive seat suspensions for vibration attenuation of vehicle occupants

Literature on biodynamic modelling of the occupant in a vehicle associates riders’ comfort with human-seat interaction forces and vibration attenuation capabilities of the suspension system. Though the superiority of active suspension systems over passive ones is well established in literature, quantification of this superiority by using the best possible passive suspension system has not been reported. This work attempts to do this. It integrates a nonlinear cushion seat contact force model and a 12 degrees of freedom two-dimensional seated human body model supported by an inclined backrest with a full vehicle model through the seat suspension system. The passive and active proportional integral derivative suspension system parameters are obtained by simultaneously minimizing the seat effective amplitude transmissibility, cushion contact force and head motion using a multi-objective genetic algorithm in MATLAB-SIMULINK co-simulation. The time responses of cushion contact force, head vertical and fore-aft motion are studied for two road profiles—random and bump. Comparative analyses were also done with regard to internal forces, absorbed power and the effect on vehicle chassis. Human body response to different grades of road roughness and vehicle speeds were investigated. The results establish the clear superiority of the active system in all aspects with rise in suspension travel and acceleration of vehicle chassis in the vertical direction for a random road profile. A parameter sensitivity analysis allowed us to identify spring stiffness as the component which needs greatest care during fabrication.

A New Switching Adaptive Fuzzy Controller with an Application to Vibration Control of a Vehicle Seat Suspension Subjected to Disturbances

This paper proposes a new switching adaptive fuzzy controller and applies it to vibration control of a vehicle seat suspension equipped with a semi-active magnetorheological (MR) damper. The proposed control system consists of three functioned filters: (1) Filter 1: a model of interval type 2 fuzzy to compensate disturbances; (2) Filter 2: a ‘switching term’ to evaluate the magnitude of disturbance; and (3) Filter 3: a group of adaptation laws to enhance the robustness of control input. These filters play a role of powerful shields to improve control performance and guarantee the stability of the applied system subjected to external disturbances. After embedding a PID (proportional-integral-derivative) model into Riccati-like equation, main control parameters are updated based on the adaptation laws. The proposed controller is then synthesized in two different cases: high disturbance and small disturbance. For the high disturbance, a special type of sliding surface function, which relates to an exponential function and its t-norm, is used to increase the energy of control system. For the small disturbance, the energy from the modified t-norm of the sliding surface is neglected to reduce the energy consumption with maintaining the desired performance. To demonstrate the effectiveness of the proposed controller, a vehicle seat suspension installed with controllable MR damper is adopted to reflect the robustness against external disturbances corresponding to road excitations. It is validated from computer simulation that the proposed controller can provide better vibration control performance than other existing robust controllers showing excellent control stability with well-reduced displacement and velocity at the position of the seat.

Semi Active Seat Suspension System using Modified Intelligent Active Force Control

This paper presents a modified intelligent active force control (AFC) control strategy in a semi active seat suspension system. The main actuator studied in this research is the Magneto-rheological (MR) damper. Since a semi-active device like MR damper can only dissipate energy so a modified version of AFC controller is needed. The modified AFC controller main function is to determine the appropriate control force. A Heaviside Step Function (HSF) is used to ensure the MR damper produce the desired damping force according to the control force generated by AFC controller. The phenomenological Bouc-Wen is used to study the effectiveness of the new AFC controller taking into account the dynamic response of the damper. Sinusoidal signals simulated as vibration sources are applied to the seat suspension system to investigate the improvement of ride comfort as well as to ascertain the new AFC controller robustness. Comparison of body acceleration signals from the passive suspension with AFC controller semi active seat suspension system shows up to to 45% improvement to the occupant ride comfort under different vibration intensities.

Experimental Study of a Variable Stiffness Seat Suspension Installed With a Compact Rotary MR Damper

Traditional MR seat suspension without stiffness control is not able to avoid the resonance between the excitation and the seat, though it can dampen the vibration energy. To solve this problem, this paper proposed a variable stiffness (VS) magnetorheological (MR) damper to implement an advanced seat suspension. Its natural frequency can be shifted away from the excitation frequency through the variations of stiffness, thereby realizing the non-resonance control. The new seat suspension is designed and prototyped first, and then its dynamic property under different energizing current, excitation amplitude, and excitation frequency was tested using an MTS machine. The testing results verified its stiffness controllability. The vibration attenuation performance of the seat suspension was also evaluated on a vibration shaking table. The vibration reduction performance of the seat suspension was evaluated under two kinds of excitations, i.e., harmonic excitation and random excitation; the experimental results indicate that the new seat suspension outperforms passive seat suspensions regarding their ride comfort.

A comparison of different models of passive seat suspensions

Long duration exposure to vehicle induced vibration causes various ailments to humans. Amongst the various components of the human-vehicle system, the seat suspension plays a major role in determining the level of vibration transferred to humans. However, optimising the suspension for maximising human comfort leads to poor vehicle handling characteristics. Thus, predicting human comfort through various seat suspension models is a widely researched topic. However, the appropriate seat suspension model to be used has not been identified so far. Neither has any prior work reported integrating models of all the components necessary for this analysis, namely human body, cushion, seat suspension and vehicle chassis, each with the appropriate level of complexity. This work uses a two-dimensional 12 DoF seated human body model with inclined backrest support, a nonlinear cushion model, a seat suspension model and a full vehicle model. Two kinds of road profiles – one with random roughness and one with a bump – have been used. It then compares the performance of five different seat suspension models based on a number of human comfort related parameters (seat to head transmissibility, suspension travel, seat acceleration, cushion contact force and head acceleration in both vertical and fore-aft directions) and vehicle handling parameters (vertical, rolling and pitching acceleration of chassis). The results clearly show the superiority of the configuration which involves a spring parallel to an inclined multi-stage damper. A separate analysis was also done to judge whether the integration of the vehicle model (with its associated complication) was necessary for this analysis. A comparison of the human body’s internal forces, moments, acceleration, and absorbed power with and without the vehicle model clearly indicates the need of using the former.

Measurement of stiffness and damping coefficient of rubber tractor tires using dynamic cleat test based on point contact model

The ride vibration of a tractor is affected mostly by the stiffness and damping coefficient of the seat suspension, cabin suspension, cabin rubber mounts, and rubber tires. However, in the case of rubber tractor tires, the stiffnesses and damping coefficients have not been researched adequately thus far, and it is not simple to measure these characteristics. In this study, a method for measuring and analyzing the stiffnesses and damping coefficients of rubber tractor tires, which were the input parameters for the tractor ride vibration simulation, was proposed. The cleat test, proposed in this study, did not require separate and complicated test equipment, unlike the conventional methods. The test was conducted simply by measuring acceleration under the driving conditions of the vehicle without detaching tires from the vehicle body or setting up additional test equipment. Based on the ground-vertical acceleration data obtained, the stiffness was calculated using the logarithmic decrement method, and the damping coefficient was calculated using least squares exponential curve fitting. The result of the cleat test indicated that the front tires had stiffnesses of 486.08-570.69 kN/m and damping coefficients of 4.02-4.52 kN·s/m; the rear tires had stiffnesses of 409.42-483.79 kN/m and damping coefficients of 2.21-2.67 kN·s/m. During the test, 40 mm height cleats were installed on the track and the speed of the tractor was set to 7 and 10 km/h, which were the most common speeds during the operation. This study is meaningful in that it has presented a new method that improves the practicality of results, reduces cost, and simplifies the test process for measuring the stiffnesses and damping coefficients of rubber tractor tires. Keywords: ride vibration, rubber tractor tire, stiffness, damping coefficient, cleat test, point contact model DOI: 10.25165/j.ijabe.20211401.5799 Citation: Yoo H, Oh J, Chung W-J, Han H-W, Kim J-T, Park Y-J, et al. Measurement of stiffness and damping coefficient of rubber tractor tires using dynamic cleat test based on point contact model. Int J Agric & Biol Eng, 2021; 14(1): 157–164.

The effects of different seat suspension types on occupants' physiologic responses and task performance: implications for autonomous and conventional vehicles

This study evaluated whole body vibration (WBV), non-driving task performance, muscle activity, and self-reported discomfort and motion sickness between different seat suspension systems in a simulated vehicle environment. In a repeated-measures laboratory experiment where field-measured 6-degree-of-freedom (6-DOF) passenger vehicle vibration was replicated on a 6-DOF motion platform, we measured WBV, non-driving task (pointing, typing, web-browsing, and reading) performance, low back (erector spinae), shoulders (trapezius) and neck (splenius capitis and sternocleido-mastoid) muscle activity, and self-reported discomfort and motion sickness from three different seats: a vertical (z-axis) active suspension, multi-axial active suspension [vertical (z-axis) + lateral (y-axis)], and a static suspension-less seat (current seat type in all passenger cars). Both the vertical and multi-axial active suspension seats significantly reduced the vertical WBV exposure (p < 0.0001). However, no significant differences were found in non-driving task performance (p > 0.30), muscle activity (p > 0.22), self-reported discomfort (p > 0.07), and motion sickness (p = 0.53) across three different seats. These findings indicate that the active suspension seats may have potential to future reduce the vertical and total WBV exposures, respectively. However, none of the suspension seats demonstrate any significant benefits on the non-driving task performance, muscle activity, self-reported discomfort and motion sickness measures in a simulated vehicle environment.

Simulation of Active Force Control Using MR Damper in Semi Active Seat Suspension System

With the rapid development of electronic sensor and actuator technology, semi-active seat suspension system has become even more practical driven by lower power consumption. Magneto-rheological (MR) dampers are among the best and the most reliable semi active control devices that can produce controllable damping force in seat suspension system to further improve the ride comfort. This paper focus on a new controller scheme named Active Force Control (AFC) to control the damping force of the MR damper to achieve better ride comfort. The phenomenological Bouc-Wen model for MR damper has been simulated in Matlab Simulink to study the effectiveness of the new AFC controller. A sinusoidal signal simulated as vibration source is applied to the seat suspension system to investigate the improvement of ride comfort as well as to ascertain the new AFC controller robustness. Comparison of body acceleration signals from the passive suspension with AFC controller semi active seat suspension system shows improvement to the occupant ride comfort under different vibration intensities.

Experimental determination of the parameters of the characteristics of the seat suspension for automotive vehicles

This article describes the methodology and results of the experimental determination of the static-elastic damping characteristics of the Sibeco air suspension with a scissor guide mechanism. To implement the measurement procedure in laboratory conditions, bench equipment, including a compressor unit (power system) with a control pressure gauge, a measuring device (height gauge) for fixing linear displacements and reference weights, was used. The measurements were carried out stepwise at various fixed values of air pressure in the pneumatic elastic element, as well as in the presence or absence of a standard unregulated hydraulic shock absorber in the design of the considered seat suspension system. The whole process of obtaining the necessary parameters was held in accordance with the recommendations of the official domestic regulatory documentation, which establishes regulations on the general technical conditions for the design of seats for automotive vehicles. There were analyzed the obtained curves of the static characteristics of the seat suspension, including for the presence of a character of nonlinearity in different specific sections of the characteristic. Based on these results, the values of the parameters of stiffness, natural frequency and resistance forces (“dry friction” forces) were calculated during the compression and rebound strokes of the seat suspension for certain measurement conditions. Additionally, an assessment for the compliance of these parameters with the normative indicators of domestic technical standards was made. Also, the dependences of the instantaneous values of the stiffness of the considered air suspension of the Sibeco seat on deformation at various air pressures in the pneumatic elastic element were constructed and analyzed. Recommendations on the operation of this device for cushioning the seats of operators of motor and tractor equipment were given.

Methods for controlling the elastic damping characteristics of pneumatic seat suspensions

The pneumatic seat suspension is one of the most important, and in some situations, one of the key components of the vibration protection system for the human operator of the vehicle. At the present stage of scientific and technical activities of most developers, great emphasis is placed on controlled seat suspension systems, as the most promising systems. This article analyzes the methods of controlling the elastic damping characteristics of the air suspension of a vehicle seat. Ten different and fairly well-known methods of changing the shape and parameters of elastic damping characteristics due to electro-pneumatic valves, throttles, motors, additional cavities, auxiliary mechanisms and other actuators were considered, the advantages, application limits and disadvantages of each method were analyzed. Based on the results of the performed analytical procedure, as well as the recommendations known in the scientific and technical literature on improving the vibration-protective properties of suspension systems, the authors proposed and developed a new method for controlling the elastic-damping characteristic, which is implemented in the proposed technical solution for the air suspension of a vehicle seat. The method differs in the thing that it implements a cyclic controlled exchange of the working fluid between the cavities of the pneumatic elastic element and the additional volume of the receiver on the compression and rebound strokes, forming an almost symmetric elastic damping characteristic, and partial recuperation of vibrational energy by a pneumatic drive, presented in the form of a rotary type pneumatic motor. In addition, the method does not require an unregulated hydraulic shock absorber, while still having the advantage of improved vibration-proof properties of the air suspension of a vehicle seat over a wide range of operating influences.

Vibration levels on operator’s workplace and vibration protection characteristics of seat suspensions

This article analyzes the nature and parameters of the main operational disturbances, which energy is directly or indirectly transferred to the operator's workplace of tractor with a caterpillar or wheeled propeller when performing various technological operations, based on experimental research data. The main operating frequency range of these operational disturbances is considered. The contribution of each frequency component to the overall level of vibration at the operator's workplace is assessed. The example of implementation the results of field measurements of real operational disturbances and vibration characteristics on a K-744R1 (st.) wheeled tractor, which operated in a unit with a PG-3-5 plane cutter in the mode of plowing stubble at a constant speed of movement was used. The comparative study of vibration-protective properties of various designs of seat suspension was carried out. The technique of field measurements, including specialized equipment of the ZETLAB and Assistant companies, the mode, the sensor installation scheme and other conditions are described. Using the numerical Runge-Kutta method and mathematical modeling tools in the Simulink MatLab software environment, the operation of the serial suspension of the K-744R1 (st.) tractor seat, air suspension of the Sibeco seat with a scissor guiding mechanism and the innovative air suspension of the seat (based on Sibeco) with controlled extraction of vibration energy and its subsequent recuperation was simulated. There were obtained the calculated oscillograms and spectra of vertical accelerations on a seat cushion, sprung with each of the considered suspensions under the input action of measured real operational disturbances. The results of the analysis of the research results are summed up.