Strut Suspension Research Articles

Stiffness Performance Simulation and Testing of a New Type Integrated Suspension Strut

The design scheme of a new type strut was put forward, whose stiffness characteristics can undertake linkage control. The structure and basic principle of this new suspension component were introduced. According to fluid mechanics and thermodynamics, a mathematical model for the stroke dependent stiffness characteristics of the strut was established, and the stiffness characteristics were analyzed by using software SIMULINK. Then the stiffness performance bench test of the strut specimen was carried out for verification. Results show that the test results agree well with the simulation results. It is verified that the established mathematical model is correct and the stiffness of this strut shows nonlinear changes vary with the displacement of piston. When the suspension is largely impacted, the stiffness of this strut increases quickly which could restrain the wheel bouncing, body roll and vertical vibration.

Vibration suppression using two-terminal flywheel. Part II: application to vehicle passive suspension

The two-terminal flywheel introduced in Part I is suggested to be attached in parallel to the suspension strut whose vibration suppression performance improvement is accordingly investigated in this paper. The passenger comfort, tire grip and suspension deflection are respectively taken as the vibration suppression indices to design the optimal parameters of the proposed and conventional passive suspensions. The optimal single-objective performances of both suspensions arecompared to each other in actual dynamic parameter ranges. Due to the three conflicting and non-commensurable performance objectives, the Chebyshev goal programming approach is subsequently applied to find a multi-objective compromise for a design case. The non-ideal factors of the inverse screw transmission mechanism, which is modeled in Part I, are also taken into consideration to discuss the influence on the vibration suppression performance. The resultsshow that, owing to the presence of the two-terminal flywheel, the proposed suspension employing this novel component significantly outperforms the conventional one in terms of both passenger comfort and tire grip, with practically identical suspension deflection performance.

Uncertainties with Respect to Active Vibration Control

The content of this work is the presentation of the prototype of a new active suspension system with an active air spring. As being part of the Collaborative Research Unit SFB805 “Control of Uncertainties in Load-Carrying Structures in Mechanical Engineering”, founded by the Deutsche Forschungsgemeinschaft DFG, the presented active air suspension strut is the first result of the attempt to implement the following requirements to an active suspension system: Harshness and wear: Reduced coulomb friction, i.e. no dynamic seal. Plug and drive solution: Connected to the electrical power infrastructure of the vehicle. Vehicle and customer application by software and not by hardware adaption. These requirements were defined at the very beginning of the project to address uncertainties in the life cycle of the product and the market needs. The basic concept of the active air spring is the dynamic alteration of the so-called effective area. This effective area is the load carrying area A of a roller bellow and defined by A:=F/(p-pa). F denotes the resulting force of the strut, p the absolute gas pressure and pa the ambient pressure. The alteration of this effective area is realized by a mechanical power transmission, from a rotational movement to four radial translated piston segments. Due to the radial movement of the piston segments, the effective area A increases and so does finally the axial compression force F. The prototype presented in this paper serves as a demonstrator to proof the concept of the shiftable piston segments. This prototype is designed to gather information about the static and dynamic behavior of the roller bellows. Measurements show the feasibility of the concept and the interrelationship between the piston diameter and the resulting spring force.

Multibody dynamics modelling and system identification of a quarter-car test rig with McPherson strut suspension

In this paper, we develop a multibody dynamics model of a quarter-car test-rig equipped with a McPherson strut suspension and we apply a system identification technique on it. Constrained equations of motion in the Lagrange multiplier form are derived and employed to characterise the dynamic behaviour of the test rig modelled once as a linear system and once as a non-linear system. The system of differential algebraic equations is integrated using a Hilber–Hughes–Taylor integrator. The responses of both models (linear and non-linear) to a given displacement input are obtained and compared with the experimental response recorded using the physical quarter-car test rig equipped with a McPherson strut suspension. The system identification is performed for control purposes. The results, as well as the performance and area of applicability of the test rig models derived, are discussed.

Sliding-mode control for semi-active suspension with actuator dynamics

A sliding-mode controller (SMC) is proposed for semi-active suspensions to achieve ride comfort and handling performance simultaneously. First, a nonlinear quarter-car model of Macpherson strut suspension is established in Matlab/Simulink. Constrained damper force and actuator dynamics are considered for the damper model. System identification is applied to the nonlinear model for obtaining the linear model parameters. Kalman filter is designed based on the linear model and the actuator dynamics to estimate the state responses required for SMC. The sliding surface consists of tyre deflection and sprung mass acceleration. The proposed SMC is evaluated using the nonlinear model for both time and frequency domain responses. Robustness due to the increased sprung mass and deteriorated suspension is also investigated in this paper. Preliminary simulation results show improved ride comfort without sacrificing the road holding performance.

An insight into linear quarter car model accuracy

The linear quarter car model is the most widely used suspension system model. A number of authors expressed doubts about the accuracy of the linear quarter car model in predicting the movement of a complex nonlinear suspension system. In this investigation, a quarter car rig, designed to mimic the popular MacPherson strut suspension system, is subject to narrowband excitation at a range of frequencies using a motor driven cam. Linear and nonlinear quarter car simulations of the rig are developed. Both isolated and operational testing techniques are used to characterise the individual suspension system components. Simulations carried out using the linear and nonlinear models are compared to measured data from the suspension test rig at selected excitation frequencies. Results show that the linear quarter car model provides a reasonable approximation of unsprung mass acceleration but significantly overpredicts sprung mass acceleration magnitude. The nonlinear simulation, featuring a trilinear shock absorber model and nonlinear tyre, produces results which are significantly more accurate than linear simulation results. The effect of tyre damping on the nonlinear model is also investigated for narrowband excitation. It is found to reduce the magnitude of unsprung mass acceleration peaks and contribute to an overall improvement in simulation accuracy.

Preliminary Step Towards Wire-Driven Parallel Suspension Systems for Static and Dynamic Derivatives of the Aircraft in Low-Speed Wind Tunnels

The wind tunnel test is one important way to obtain the aerodynamic derivatives of aircrafts. These derivatives are necessary when the guidance and control systems of the aircraft are designed and when the dynamic quality of the aircraft is analyzed as well. The results of experiments of the static derivatives and dynamic derivatives of the aircraft in low-speed wind tunnels have revealed that there are some unavoidable drawbacks such as the interference of the streamline flow brought about by the strut in the traditional strut suspension system. A cable-mounted system is very suitable for experiments of the static derivatives of an aircraft, but it cannot be used in the experiments of dynamic derivatives. In order to use the same wire-driven parallel suspension system to realize the static and dynamic derivates experiments in low-speed wind tunnels, a survey of the research work addressed within the Wire-Driven Parallel Suspension Systems (WDPSS-8) project is presented in this paper. The results show that WDPSS-8 can be successfully used in experiments of static derivatives, and that it has potentiality to be used in experiments of dynamic derivatives. In the issues in the theoretical aspect the issues have been handled. However, much work should be done in the experimental aspects. The research outcomes of WDPSS-8 will help the Chinese set up Chinese brands in the field of wind tunnel tests of aircrafts.

Roll- and pitch-plane coupled hydro-pneumatic suspension

Passive fluidically coupled suspensions have been considered to offer a promising alternative solution to the challenging design of a vehicle suspension system. A theoretical foundation, however, has not been established for fluidically coupled suspension to facilitate its broad applications to various vehicles. The first part of this study investigates the fundamental issues related to feasibility and properties of the passive, full-vehicle interconnected, hydro-pneumatic suspension configurations using both analytical and simulation techniques. Layouts of various interconnected suspension configurations are illustrated based on two novel hydro-pneumatic suspension strut designs, both of which provide a compact design with a considerably large effective working area. A simplified measure, vehicle property index, is proposed to permit a preliminary evaluation of different interconnected suspension configurations using qualitative scaling of the bounce-, roll-, pitch- and warp-mode stiffness properties. Analytical formulations for the properties of unconnected and three selected X-coupled suspension configurations are derived, and simulation results are obtained to illustrate their relative stiffness and damping properties in the bounce, roll, pitch and warp modes. The superior design flexibility feature of the interconnected hydro-pneumatic suspension is also discussed through sensitivity analysis of a design parameter, namely the annular piston area of the strut. The results demonstrate that a full-vehicle interconnected hydro-pneumatic suspension could provide enhanced roll- and pitch-mode stiffness and damping, while retaining the soft bounce- and warp-mode properties. Such an interconnected suspension thus offers considerable potential in realising enhanced decoupling among the different suspension modes.

New model and simulation of Macpherson suspension system for ride control applications

The main purpose of this paper is to propose a new nonlinear model of the Macpherson strut suspension system for ride control applications. The model includes the vertical acceleration of the sprung mass and incorporates the suspension linkage kinematics. This two-degree-of-freedom (DOF) model not only provides a more accurate representation of the Macpherson suspension system for control applications in order to improve the ride quality, but also facilitates evaluation of the suspension kinematic parameters, such as camber, caster and king-pin angles as well as track alterations on the ride vibrations. The performances of the nonlinear and linearised models are investigated and compared with those of the conventional model. Besides, it is shown that the semi-active force improves the ride quality better than active force, while the opposite is true in terms of improving the performance of the kinematic parameters. The results of variations of the kinematic parameters based on the linear model subject to road disturbances are compared with those of a virtual prototype of Macpherson suspension in ADAMS software. The analytical results in both cases are shown to agree with each other.

Handling and Braking Analyses of a Heavy Vehicle with a Cross-Axle Fluidically-Coupled Suspension

The handling and braking responses of a heavy vehicle equipped with a cross-axle fluidically-coupled hydropneumatic suspension concept are investigated. The proposed fluidically-coupled suspension is conceived by diagonally interconnecting different hydraulic fluid chambers of the four suspension struts of the vehicle. The analytical formulations of suspension forces are derived based on fluid flows through the couplings and damping valves. A generalized full-vehicle model is developed and validated to evaluate the handling and braking responses to two critical vehicle maneuvers: (i) braking-in-a-turn; and (ii) split-μ straight-line braking. The responses of the vehicle model with the coupled suspension are compared with those of the uncoupled suspension under various inputs to demonstrate the potential benefits of the proposed cross-axle fluidic coupling of the suspension struts.

Pitch plane analysis of a twin-gas-chamber strut suspension

A twin-gas-chamber hydropneumatic suspension strut concept is proposed to achieve enhanced bounce and pitch ride, and pitch attitude control. The response characteristics of the twin-gas-chamber strut suspension are compared with those of a single-gas-chamber strut suspension to demonstrate not only superior performance potentials but also the added design flexibility offered by the twin-gas-chamber struts. The relative responses of both strut suspensions are evaluated through analysis of a pitch plane vehicle model, subject to straight-line braking inputs and excitations arising from randomly distributed road elevations. A generalized formulation for the strut forces is presented to derive the bounce and pitch rates of the proposed strut suspensions. The results reveal that the twin-gas-chamber strut suspension exhibits a slightly lower pitch stiffness in the vicinity of design ride height, but progressively hardening effects with increasing pitch deflections. Moreover, the twin-gas-chamber strut suspension exhibits considerably fewer hardening—softening effects in suspension rate compared with the suspension involving the single-gas-chamber struts. The results attained from the parametric studies are also discussed to demonstrate superior design flexibility of the twin-gas-chamber struts for tuning of the suspension bounce and pitch stiffness properties. The dynamic responses of the vehicle model with different suspensions are assessed subject to random road roughness excitations as well as braking torque inputs. The results demonstrate that the twin-gas-chamber strut suspension offers considerable potential for enhancing bounce and pitch ride, pitch attitude control, and suspension travel responses under braking, while the influence on the ride and road-holding responses under random road inputs is insignificant. The results also suggest that a relatively soft front suspension design could provide further enhancement of pitch ride and pitch deflection responses under random road roughness excitations.

Mode and design sensitivity analyses for brake judder reduction

Brake judder is a phenomenon that occurs when the steering wheel vibrates abnormally owing to braking at a high speed. It is classified into cold and hot judders. The former is generated because of an initial uneven disc surface and the latter results from uneven heat spots on the disc surface by braking repeatedly. There are two ways to reduce the judder. One is to reduce the excitation by modification of the disc shapes and pad ingredients. The other is to improve modal characteristics of the suspension system. The latter approach is used in this research. Real vehicle tests and computer simulation are utilized to analyse systematically the judder phenomenon of the vehicle. The Macpherson strut suspension is employed, and the judder sensitivity is calculated on the basis of a design sensitivity analysis. The bush stiffness is reworked and a braking test is carried out to verify the sensitivity result. Judder reduction by the mode control is verified.

실시간 다물체 차량 해석을 위한 준정적법의 컴플라이언스 효과 모델링

Compliance effect consideration method for real-time multibody vehicle dynamics is proposed using quasi-static analysis. The multibody vehicle model without bush elements is used based on the subsystem synthesis method which provides real-time computation on the multibody vehicle model. Reaction forces are computed in the suspension subsystem. According to deformation from the quasi-static analysis using reaction forces and bush stiffness, suspension hardpoint locations and suspension linkage orientation are changed. To validate the proposed method, quarter car simulations of McPherson strut and multilink suspension subsystems are performed. Full car bump run simulations and fish hook handling test simulations are also carried out comparing with the ADAMS vehicle model with bush elements. CPU times are also measured to see the real-time capabilities of the proposed method.

실시간 차량 동역학 해석을 위한 안티 롤 바 힘 계산 알고리듬

Anti roll bar model for real time multibody vehicle dynamics model has been proposed using kinematic constraint. Anti roll bar have been modeled by kinematic relationship, and mass properties are neglected. Relative angle of torsion bar spring is computed by constraint about drop-link using Newton-Raphson iteration, and then the torque of torsion bar spring can be computed with the angle and torsion spring stiffness. Finally anti roll bar force acting on both knuckle can be calculated. To validate the proposed method, half car simulations of McPherson strut suspension and full car simulations are also carried out comparing with the ADAMS vehicle model with anti roll bar. CPU times are also measured to see the real-time capabilities of the proposed method.

Optimized design for a MacPherson strut suspension with side load springs

Undesired lateral force inevitably exists in a MacPherson suspension system, which is liable to damper rod’s side wear and promotes the damper’s inner friction decreasing the ride performance from the suspension system. Substituting a new side load spring with curved centerline for the conventional coil spring has been proven able to solve these problems and Multi-body Dynamics combining with Finite Elements Analysis may be an efficient method in optimizing its design. Therefore, taking a passenger car as example, a detailed multi-body dynamics model for the suspension system is built to simulate forces exerted on the damper and the minimization of its lateral component is selected as the design target for the spring. When the structure optimization of the side load spring is performed using FEA software ANSYS, its vertical and lateral elastic characteristics, supported by test data, are analyzed. After importing FEA results back to the suspension system, the dynamics simulation can be performed to validate the optimization result.

Decomposition approach to model smart suspension struts

Model and simulation study is the starting point for engineering design and development, especially for developing vehicle control systems. This paper presents a methodology to build models for application of smart struts for vehicle suspension control development. The modeling approach is based on decomposition of the testing data. Per the strut functions, the data is dissected according to both control and physical variables. Then the data sets are characterized to represent different aspects of the strut working behaviors. Next different mathematical equations can be built and optimized to best fit the corresponding data sets, respectively. In this way, the model optimization can be facilitated in comparison to a traditional approach to find out a global optimum set of model parameters for a complicated nonlinear model from a series of testing data. Finally, two struts are introduced as examples for this modeling study: magneto-rheological (MR) dampers and compressible fluid (CF) based struts. The model validation shows that this methodology can truly capture macro-behaviors of these struts.

The "Drumhead" Graft Repair of Deep Nasal Alar Defects

Extirpation of tumors on the perialar region often results in deep surgical defects. The nares and internal nasal valves are supported not just by alar cartilage, but also by the suspension effect of the overlying skin and subcutaneous tissue. Surgical loss of tissue may result in inward collapse of the nasal vestibule with resultant difficulty in breathing. The use of full-thickness skin grafts (FTSGs) on deep alar defects commonly results in a sunken or depressed graft that is functionally and cosmetically unacceptable. We describe a novel technique that enables the use of FTSGs in the repair of deep nasal alar defects through the application of an overlying, rigid plastic suspension strut coupled with an undersized graft. The drumhead FTSG is effective in preventing collapse of the nasal vestibule as well as undesirable contour irregularities due to a depressed or sunken graft. Patients were seen at 1 week, 4 weeks, and 3 months postoperatively. At each time point, there was no nasal vestibular collapse and only very slight graft depression, which replicated the normal mild concavity of the alar crease region. All patients had excellent functional and cosmetic outcomes. No adverse effects were noted. The "drumhead" graft is a novel technique, which enables the use of FTSGs for deep alar defects by inhibiting undesirable depression of the graft and preventing collapse of the nasal vestibule.

Liquid Spring Shock Absorber with Controllable Magnetorheological Damping

An automotive suspension strut is investigated that utilizes compressible magnetorheological (CMR) fluid. A CMR strut consists of a double-ended rod in a hydraulic cylinder and a bypass comprising tubing and an MR valve. The diameter of the rods on either side of the piston are set to be different in order to develop spring force by compressing the MR fluid hydrostatically as a result of varying shaft volume in the hydraulic cylinder. The MR bypass valve is adopted to develop a controllable damping force. A hydromechanical model of the CMR strut is derived by considering lumped hydraulic parameters such as compliances of chambers inside the cylinder and flow resistances through the MR bypass valve. The spring force and nominal spring rate owing to fluid compressibility and the controllable flow resistance and pressure drop in the bypass were analytically investigated on the basis of the model. Finally, a CMR strut, filled with silicone oil-based MR fluid, is fabricated and tested. The spring force and variable damping force of the CMR strut are clearly observed in the measured data, and compare favourably with the analytical model. Additionally, characteristics of a double-rod strut whose rod diameters are the same, so that the shaft volume in the hydraulic cylinder is constant, are analysed and compared with a CMR strut whose rod diameters are different.

Effect on compliance and alignment variation with respect to stiffness of knuckle and shock absorber in a McPherson strut suspension

Suspension compliance, compliance steer and wheel alignment variation are very important to improve a vehicle’s stability, controllability and ride comfort. Naturally, the degree of precision with the calculation for those elements is essential. In case of the McPherson strut suspension, a shock absorber and a knuckle are exposed to the bending force from the tyre, and the stiffness has an effect on the compliance, compliance steer and wheel alignment variation. In fact, we are often forced to change the design values relating to suspension geometry and bush characteristics. This article describes a new computing system that has been developed to calculate the effect of the stiffness of a shock absorber and a knuckle on the compliance, compliance steer and wheel alignment variation per second in a simple way, and to clarify the effect.

Performance Benefits in Passive Vehicle Suspensions Employing Inerters

A new ideal mechanical one-port network element named the inerter was recently introduced, and shown to be realisable, with the property that the applied force is proportional to the relative acceleration across the element. This paper makes a comparative study of several simple passive suspension struts, each containing at most one damper and inerter as a preliminary investigation into the potential performance advantages of the element. Improved performance for several different measures in a quarter-car model is demonstrated here in comparison with a conventional passive suspension strut. A study of a full-car model is also undertaken where performance improvements are also shown in comparison to conventional passive suspension struts. A prototype inerter has been built and tested. Experimental results are presented which demonstrate a characteristic phase advance property which cannot be achieved with conventional passive struts consisting of springs and dampers only.