Full vehicle simulation using thermomechanically coupled hybrid neural network shock absorber model

In the case of full vehicle models, the technique of multi-body simulation (MBS) is frequently used to study their highly non-linear dynamic behaviour. Many non-linearities in vehicle models are induced by force elements like springs, shock absorbers, bushings and tires. Commonly, spline functions are used to represent the force responses of these components. If the non-linear relationships are more complicated, the spline approximations are no more accurate. An alternative approach is based on empirical neural networks which are based on the mathematical approximation of measured data. It is well known that neural networks are able to represent and predict complex component responses accurately. The aim of this paper is to perform a dynamic full vehicle simulation using a thermomechanically coupled hybrid neural network shock absorber model. In this shock absorber model, the spline approach is combined with a temperature-dependent neural network. Based on a displacement-controlled excitation on a four post test rig in the ADAMS/Car MBS software, a rugged test track is simulated. In this way, the front and rear shock absorbers are dynamically loaded with comfort-relevant frequencies in the range of 0.75–30 Hz and velocity amplitudes up to 2 m/s. By the simulation, stability of the hybrid neural network model is demonstrated. Furthermore, the damping force, the vertical acceleration of the chassis and the required simulation times are compared. The standard spline approach is used as a reference.     

Hybrid neural network model for history-dependent automotive shock absorbers

The method of numerical multi-body simulation is an often used and well-understood development tool in the automotive industry. In order to reproduce the ride comfort or handling behaviour of vehicles, mathematical models have to be built up. To achieve accurate simulation results, highly detailed component models are required. However, the formulation of appropriate physically-based model equations of complex automotive components (e.g. air springs, shock absorbers, rubber bearings, tyres, etc.) can be very difficult. To handle this, empirical modelling methods have been developed. Simple algebraic equations are used to describe complex system behaviour. This simplification is very effective, although it largely ignores the natural laws of mechanics and thermodynamics but is still capable to predict the component response. This article illustrates how to take advantage of this approach in numerical simulations. We describe the development of a hybrid automotive shock absorber model based on both spline and neural network (NN) approaches. By combining these different approaches, an accurate model is achieved without loss of variability. Non-isothermal laboratory force-displacement measurements of an automotive shock absorber are being used to estimate the parameters of the NN. As shown, the model replicates the measured data with sufficient accuracy, especially the hysteresis. Finally, we present a set of quarter-car simulations with a built-in hybrid NN shock absorber.     

On the performance of rheological shock absorber models in full vehicle simulation

A comparative study of the performance of three rheological automotive shock absorber models as well as of an extended force–velocity relation in full vehicle simulation is performed. Simulation results for both the shock absorber test rig and a full vehicle crossing a single obstacle are compared with measured data. While the gain of accuracy by the extended force–velocity relation is marginal, the rheological models in general yield a noticeable improvement, which, however, in full vehicle simulation is less significant than in test rig simulation. Among the rheological models studied here, the one consisting of a nonlinear spring–dashpot element with an element modelling friction by a continuous transition from the compression to the extension range in parallel and a quadratic approximation of the static gas force exhibits the best global performance.     

Investigation of Cavitation Process in Monotube Shock Absorber

The paper investigates cavitation effect which negatively influences the performance of a monotube shock absorber of road vehicle (passenger car). For better understanding of this phenomena, three physical models of shim stack valves are analyzed. Validation results allowed selecting the most appropriate valve model in presence of cavitation processes. A mathematical model of monotube damper with consideration of fluid compressibility and cavitation phenomena is developed. Simulation results are validated by experimental data obtained on hydraulic test rig. Based on the selected approach, a simplified method suitable for assessment of cavitation processes in automotive monotube shock absorbers is proposed. After investigation it is found that damping force when cavitation occurs mainly depends on the initial pressure and absorber inner diameter.     

A Thermomechanically Coupled Model for Automotive Shock Absorbers: Theory, Experiments and Vehicle Simulations on Test Tracks

In the development of cars numerical simulation plays a more and more important role. A method commonly used in this context is based on the formalism of multibody dynamics. In this approach a vehicle is described as a system of rigid bodies connected by joints, bushings, springs and dampers. For the purpose of estimating the time-dependent dynamical loads when riding, for example, over potholes or other obstacles we need enhanced models representing the mechanical behavior of the shock absorbers. A model of this type should describe the nonlinear rate dependence of the force in combination with friction effects and thermomechanical coupling phenomena. Due to the dissipation of energy the temperature of the shock absorber increases and influences its damping behavior. When riding over long rugged test tracks these effects are strongly pronounced. Thus we develop a thermomechanical model representing all these phenomena with good approximation and being compatible with the natural laws of thermodynamics. To validate the theory, we investigate the thermomechanical behavior of two automotive shock absorbers in detail. We measure the velocity dependence of the force under different temperature levels as well as the dissipative change in the temperature during cyclic excitations. Finally we carry out a vehicle test on a rugged test track and record the temperature of the front and rear dampers. As we show, the model describes all phenomena with sufficient approximation, especially the evolution of temperature.     

A Thermomechanically Coupled Model for Automotive Shock Absorbers: Theory,Experiments and Vehicle Simulations on Test Tracks

In the development of cars numerical simulation plays a more and more important role. A method commonly used in this context is based on the formalism of multibody dynamics. In this approach a vehicle is described as a system of rigid bodies connected by joints, bushings, springs and dampers. For the purpose of estimating the time-dependent dynamical loads when riding, for example, over potholes or other obstacles we need enhanced models representing the mechanical behavior of the shock absorbers. A model of this type should describe the nonlinear rate dependence of the force in combination with friction effects and thermomechanical coupling phenomena. Due to the dissipation of energy the temperature of the shock absorber increases and influences its damping behavior. When riding over long rugged test tracks these effects are strongly pronounced. Thus we develop a thermomechanical model representing all these phenomena with good approximation and being compatible with the natural laws of thermodynamics. To validate the theory, we investigate the thermomechanical behavior of two automotive shock absorbers in detail. We measure the velocity dependence of the force under different temperature levels as well as the dissipative change in the temperature during cyclic excitations. Finally we carry out a vehicle test on a rugged test track and record the temperature of the front and rear dampers. As we show, the model describes all phenomena with sufficient approximation, especially the evolution of temperature.     

On the performance of rheological shock absorber models in full vehicle simulation

A comparative study of the performance of three rheological automotive shock absorber models as well as of an extended force-velocity relation in full vehicle simulation is performed. Simulation results for both the shock absorber test rig and a full vehicle crossing a single obstacle are compared with measured data. While the gain of accuracy by the extended force-velocity relation is marginal, the rheological models in general yield a noticeable improvement, which, however, in full vehicle simulation is less significant than in test rig simulation. Among the rheological models studied here, the one consisting of a nonlinear spring-dashpot element with an element modelling friction by a continuous transition from the compression to the extension range in parallel and a quadratic approximation of the static gas force exhibits the best global performance.     

汽车筒式液阻减振器技术的发展

分析了汽车乘坐舒适性／行驶平顺性和操作稳定性对筒式液阻减振器特性的要求，提出汽车在不同行驶工况减振器特性的要求是不的；分析了被动式减振器的发展历程及非充气和充气减振器的特点，阐述了机械控制式可调阻尼减振器，电子控制式减振器以及电流变和磁流变液体减器等的结构特点，工作原理及其动态特性；分析了筒式液阻减振器其于经验设计／实验修正开发方法的缺点，阐述了基于CAD／CAE技术的现代设计开发方法的过程及其关键问题，最后分析了我国筒式液阻减振器技术的发展状况及问题，展望了减振器技术的发展前景。     

Technology for measuring and diagnosing the damping force of shock absorbers and the constant of coil springs when mounted on a vehicle

Diagnosis of the individual function of shock absorbers and coil springs has been simplified by an off-the-car-type tester. We studied methods of analyzing coil springs and shock absorbers independently without removing them from the vehicle. The damping force of the shock absorber itself, excluding the spring effect, can be indicated according to the axle weight/road wheel at the point of displacement 0.     

Experimental Characterization of Damping Force in Shock Absorbers with Constant Velocity Excitation

For the characterization of shock absorbers, which are intrinsically non-linear, it was considered advisable to use the 3D representation of force vs velocity-displacement domain rather than traditional force vs velocity or force vs displacement. Experimental apparatus was therefore designed and constructed to measure the damping force produced by shock absorbers. Data were processed with software suitable for fitting the experimental data functions of several variables. Experiments showed that 3D representation of restoring force allows the non-linearity of shock-absorber damping to be examined more thoroughly.     

电流变阻尼半主动控制悬架系统的设计

汽车悬架减振器对于保证车辆的乘坐舒适性和安全稳定性都具有重要作用,但目前普遍应用的被动式减振器因其力学性能不能调节,存在只能在两种性能之间折衷的先天不足,而智能半主动悬架系统方案基于“大系统多级递阶——子系统神经网络自适应”控制算法。并利用MATLAB＋Simulink对新型智能半主动悬架系统进行了仿真试验．试验结果表明系统在实现了提高车辆乘坐舒适性能的同时兼顾了安全稳定性的目的。同时由于采用电流变液减振器,使系统本身具有实时采集、响应迅速、智能化、减振降噪效果好等特点。     

键合图理论在汽车纵向角振动主动控制中的应用

本文应用键合图理论建立了汽车5自由度振动系统的键图模型并推导出状态方程，以垂直振动、纵向角振动能量最小和控制能量最小为目标函数，利用状态反馈原理代化出前悬架减振器的最佳控制力，对汽车驶过三角形单凸起时的振动响应进行了计算机仿真分析。结果表明，具有主动控制悬架的汽车，其纵向角振动得到明显的衰减。     

A NARX damper model for virtual tuning of automotive suspension systems with high-frequency loading

A computationally efficient NARX-type neural network model is developed to characterise highly nonlinear frequency-dependent thermally sensitive hydraulic dampers for use in the virtual tuning of passive suspension systems with high-frequency loading. Three input variables are chosen to account for high-frequency kinematics and temperature variations arising from continuous vehicle operation over non-smooth surfaces such as stone-covered streets, rough or off-road conditions. Two additional input variables are chosen to represent tuneable valve parameters. To assist in the development of the NARX model, a highly accurate but computationally excessive physical damper model [originally proposed by S. Duym and K. Reybrouck, Physical characterization of non-linear shock absorber dynamics, Eur. J. Mech. Eng. M 43(4) (1998), pp. 181–188] is extended to allow for high-frequency input kinematics. Experimental verification of this extended version uses measured damper data obtained from an industrial damper test machine under near-isothermal conditions for fixed valve settings, with input kinematics corresponding to harmonic and random road profiles. The extended model is then used only for simulating data for training and testing the NARX model with specified temperature profiles and different valve parameters, both in isolation and within quarter-car vehicle simulations. A heat generation and dissipation model is also developed and experimentally verified for use within the simulations. Virtual tuning using the quarter-car simulation model then exploits the NARX damper to achieve a compromise between ride and handling under transient thermal conditions with harmonic and random road profiles. For quarter-car simulations, the paper shows that a single tuneable NARX damper makes virtual tuning computationally very attractive.     

一种新型汽车减振器优化设计方法研究

在对磁流变液减振器理论模型进行分析的基础上,确定了影响磁流变液减振器性能的结构参数。将磁流变液的非线性磁特性与非牛顿流体力学性能相结合,建立了以降低磁流变液减振器响应时间常数、增加其调节比为目标函数的优化模型。根据优化结果,研制了一种新型车用磁流变液减振器,并进行了验证试验。     

节流式磁流体阻尼可调减震器的试验研究

本文介绍了以两种不同的磁流体作为工作液的节流式磁流体阻尼可调减震器的外特性试验，试验结果表明：其中ＢＨ－１磁流体的粘－磁性能和粘－温性有均优于０６－Ａ，满足了磁流体阻尼可调减震器的性能的要求，节流式磁流体阻尼可调减震器的示功图饱满，阻尼力变化显著，可调性能优良；其结构合理，为实用型磁流体阻尼可调减震器的研究奠定了良好的基础。     

Preview-Based Control of Suspension Systems for Commercial Vehicles

An active suspension with preview is developed for the rear axle of a commercial vehicle. The obtained improvements are promising and justify further investigation of the more feasible semi-active suspensions with preview. The inherent non-linearity of semi-active suspensions with switching shock absorbers and the need for controllers that can handle a broad class of control objectives has led to the development of several numerical control methods for both multi-level and continuously variable shock absorbers. The most promising control method and shock absorber type are selected and mounted in a test vehicle. Some first experimental results are discussed.     

基于键合图模型的汽车悬架减振器失效分析

应用键合图法建立整车模型,将整车模型进行Simulink转化,在仿真模型中对减振器失效引起的汽车振动变化情况进行分析研究,提出一种新的汽车悬架减振器失效分析与评价方法。     

Preview-Based Control of Suspension Systems for Commercial Vehicles

An active suspension with preview is developed for the rear axle of a commercial vehicle. The obtained improvements are promising and justify further investigation of the more feasible semi-active suspensions with preview. The inherent non-linearity of semi-active suspensions with switching shock absorbers and the need for controllers that can handle a broad class of control objectives has led to the development of several numerical control methods for both multi-level and continuously variable shock absorbers. The most promising control method and shock absorber type are selected and mounted in a test vehicle. Some first experimental results are discussed.     

车用减振器的外特性建模与仿真

针对某轿车的弹性阀片和弹簧结合型减振器的结构形式，建立了减振器复原行程开阀前、开阀后及压缩行程的阻尼力力学模型，推导出了减振器阻尼力的计算公式，并通过计算机仿真得出该轿车减振器的模拟工作特性。计算机仿真和生产实践证明，所建立的数学模型是正确的，计算方法也符合实际要求。     

麦弗逊悬架减振器侧向力分析综述

麦弗逊悬架减振器侧向力对减振器寿命和悬架性能影响很大,系统分析减振器侧向力对麦弗逊悬架设计具有重要意义。减振器的侧向力取决于车辆运动时受到的地面的作用力和悬架的几何结构,本文综述了车辆行驶时车轮上下运动的侧向力、加速、减速、转弯时侧向力的分析,确定了麦弗逊悬架的几何结构对减振器侧向力的影响因素,并通过国内外最新产品的实例说明通过改变悬架的几何结构来减小减振器侧向力的具体方法和产生的效果。最后对减振器侧向力进行了总结,并对未来麦弗逊悬架的研发工作提出了一些建议。