A 3D Brush-type Dynamic Tire Friction Model

The use of advanced dynamic friction models can improve the brush-type tire friction models. This paper presents a 3D dynamic brush model based on the LuGre friction model. The model describes the dynamics of longitudinal and lateral tire friction forces, as well as the self aligning torque dynamics. It has been originally derived in a distributed-parameter form, and then transformed to a simpler lumped-parameter form with only three internal states. Both uniform and non-uniform normal pressure distributions are considered. The model has analytical solution for steady-state conditions. The steady-state behavior is validated with respect to “magic” formula static model, which served as an “ideal” benchmark. The lumped model dynamic behavior is validated by comparing its time-responses with original distributed model responses. The model parameterization with respect to normal force and other tire/road parameters is considered as well.     

Performance of Low-bandwidth, Semi-active Damping Concepts for Suspension Control

Active damping has been shown to offer increased suspension performance in terms of vehicle isolation, suspension packaging, and road-tire contact force. It can even approximate the performance of full state feedback control without requiring the difficult measurement of tire deflection. Many semi-active damping strategies have been introduced to approximate the response of active damping with the modulation of passive damping parameters. These strategies have typically required a relatively high bandwidth for actuator response. This paper investigates the simulation performance and “frequency response” of two concepts in low-bandwidth semi-active suspension control, one that sets a damping force directly and another that sets the damping resistance. The electronically controlled bandwidth of these actuators is approximately an order of magnitude less than other semi-active devices; high frequency control is handled mechanically. A quarter-car model is studied with the controlled damping replacing both passive and active damping of typical control schemes. Both low-bandwidth damping strategies perform remarkably well compared to both active and high-bandwidth, semi-active damping. In certain dynamic performances, the new semi-active strategies outperform active damping and what the author calls “nominal” semi-active damping.     

Optimal Performance of Variable Component Suspensions

Most vehicle suspension systems use fixed passive components that offer a compromise in performance between sprung mass isolation, suspension travel, and tireroad contact force. Recently, systems with discretely adjustable dampers and air springs been added to production vehicles. Active and semi-active damping concepts for vehicle suspensions have also been studied theoretically and with physical prototypes. This paper examines the optimal performance comparisons of variable component suspensions, including active damping and full-state feedback, for “quartercar” heave models. Two and three dimensional optimizations are computed using performance indicators to find the component parameters (control gains) that provide “optimal” performance for statistically described roadway inputs. The effects of performance weighting and feedback configuration are examined. Active damping is shown to be mainly important for vehicle isolation. A passive vehicle suspension can control suspension travel and tire contact force nearly as well as a full state feedback control strategy.     

Nonlinear Design Approach to Four-Wheel-Steering Systems Using Neural Networks

Four-wheel-steering (4WS) systems have been studied and developed with remarkable success from the viewpoint of vehicle dynamics. Most of the control methods require a linearized bicycle model of the actual vehicle system which is however strongly influenced by tire nonlinearity. This paper proposes a new method to design the 4WS system taking into account the nonlinear characteristics of tires and suspensions. For this purpose integration of artificial neural network and linear control theory is introduced for the identification and control of a nonlinear vehicle model structured using a software for multi-body dynamic analysis (ADAMS). This model takes into account the nonlinear characteristics of actual vehicles with tires modeled by “magic formula“. The results of computer simulations show that the proposed nonlinear approach is efficient in improving the handling and stability of vehicles.     

Recent Research and Development on Advanced Technologies of High-Speed Railways in Japan

Summary This report outlines the rolling stock of “Shinkansen” and conventional “narrow-gauge” railways, and reviews the research and development to put railway vehicles into revenue service from the viewpoint of rolling stock dynamics in Japan.     

Energy Flow in Active Attitude Control Suspensions: A Bond Graph Analysis

Fully active ground vehicle suspensions which completely replace the passive spring and damper elements with a force generating actuator have required a significant amount of power. Alternative systems which retain compliant elements to handle high frequency isolation but include active elements to control the vehicle body attitude have been developed to reduce the power requirements. These suspensions are called “low bandwidth” or “fast load leveler” systems and they often incorporate semi-active dampers which produce high frequency controllable forces with low power requirements. Here, two contrasting attitude control systems are studied to show that actuator power can be significantly reduced if the actuator is used to vary a lever ratio instead of being used to compress the suspension spring directly. Both types of systems have been successfully implemented in prototype form. Bond graphs for idealized versions of the suspensions show clearly the significant differences in actuator power and energy requirements even though the abstract mathematical structures of the two systems are remarkably similar. Computer simulations confirm the analytical results.     

Dynamic Simulation of Taipei EMU Train

Simplified train dynamics for the trains of the Taipei Metro are presently being studied, with the aid of numerical methods, to avoid possible dangerous conditions of coupler failure and to understand the deformation of the “mechanical fuse” in a train collision. A multiple degree-of-freedom system is utilized to simulate the EMU train. Equations of motion are set up in a matrix and solved to calculate the transient responses of the couplers. Analytical solutions are checked by comparison with the results of the Runge-Kutta method. Energy absorption devices such as the coupler and the “mechanical fuse” as well as the vehicle body structure are taken into consideration to complete an integrated study of the structural crashworthiness. It is found that sudden failure of couplers would not happen for a train at coupling speeds up to 5 km/h. Coupler force for a train running at a normal acceleration from the start or at an emergency stop are also investigated. In addition, it is found that damage is confined to the fuse structures and the fuse deformation is less than the maximum allowable deformation designed in the trains, under an impact speed of 25 km/h.     

Achievable Dynamic Response for Automotive Active Suspensions *

A complete set of constraints is derived for the road disturbance transfer functions in a quarter car model of an automotive active suspension, for typical choices of measured outputs. It is shown that any road disturbance responses which are achievable using “full state feedback” can be achieved, to within an arbitrary small tolerance, using a dynamic compensator measuring suspension deflection only. Also considered are the disturbance responses to loads acting on the sprung mass, and a complete set of constraints is derived for these. It is shown that road disturbance and load disturbance responses can be determined independently if suspension deflection and sprung mass velocity are measured. Indeed, any responses achievable separately with “full measurements” can be approximated together to an arbitrary small tolerance. Certain integral relationships are shown to follow from the derived transfer function constraints. These relationships imply fundamental limitations for certain responses (e.g. tyre deflection) no matter what measurements are available for feedback.     

Static Turning Analysis of Vehicles Subject to Externally Applied Forces - A Moment Arm Ratio Formulation

A formulation for representing the static turning response of a two-axle vehicle due to applied external or control forces is expressed in terms of a simple ratio of two distances along the vehicle longitudinal axis. The two distancescoincide with points on the vehicle at which externally applied/ control forces and their reactive inertial forces act with respect to the vehicle neutral steer point. The resulting formulation is equivalent to the rotational equilibrium equation written with respect to the neutral steer point. The method allows a simple “visual analysis” of the steady turning process by showing how key forces and associated moment arms can change with respect to one another due to vehicle modifications or different operatingconditions, thereby affecting the static turning response of the vehicle.     

Longitudinal Oscillations of Vehicle/Trailer Combinations Induced by Overrun Braking

A mathematical model for the representation of longitudinal oscillations which can occur in car/trailer systems in braking, when the trailer brakes are applied through compression of the towing hitch, is described. The model is used to show how the trailer braking system parameters affect the steady deceleration performance of the vehicle combination, and the stability, in the linear system sense, of the steady motions. The sensitivity of the stability to other system design parameters is also examined.

Digital simulation of the motions occurring in response to a step input of car braking torque is reported, with the results confirming the predictions of the linear stability analysis, and also showing the influence of backlash in the trailer brake actuating mechanism.

The system is shown to be capable of self-excitation in a “shunting” mode, in which the car and trailer motions are in antiphase, with the stability/damping property critically dependent on drawbar damping, and only weakly dependent on other system parameters. The characteristic frequency of the “shunting” mode oscillations is shown to be controllable via the stiffness of the trailer brake linkage, but this frequency is closely related to the steady drawbar deflection which occurs in uniform deceleration.

The model behaviour described provides a basis for the design of relevant systems whose longitudinal dynamic characteristics will be satisfactory.     

The Available Methods to Calculate the Wheel/Rail Forces in Non Hertzian Contact Patches and Rail Damaging

In the present paper, the methods used in railway dynamics to take into account the non Hertzian multi contact patches occurring on a wheel, are summarised. Some application cases are presented as well as an explanation of the so called “squat” rail deterioration.     

Selfexcited Vibrations of the Tire

In this paper a mechanical work of external forces and torques, acting on the tire has been considered. A theory has been developed for the prediction of necessary conditions for selfexciting vibrations. The theory establishes, that the mechanical work of external forces and torques must be positive, or, what is equivalent, that the tire has to transmit energy from external environment to vehicle. The work of forces and torques has been considered as a convolution of functions, which next has been submitted to Laplace transformation. The condition of selfexcitation of vibrations, obtained from above in the frequency domain, establishes, that the imaginary part of all eigenvalues of frequency response matrix must be negative. As an example, the ranges of selfexcited vibrations of the tire have been calculated. The tire has been treated as a stretched circular string. Four different models have been considered. Three of them have been massles (kinematic), namely Pacejka's model, Von Schlippe's model and single-point model. As fourth model the dynamic Pacejka's model has been considered. The influences of longitudinal deflections on the shimmy tendency have been studied for all models

Frequency response characteristics have been numerically computed and compared for all models. A critical speed and a critical reduced frequency of first and second kind have been defined. Admissible, negative, imaginary parts of the eigenvalues of frequency response matrix have been established. These admissible values of imaginary parts of eigenvalues assure, that the energy absorbing does not excite shimmy vibrations.     

车辆-模数式伸缩缝耦合振动与冲击荷载分析

为研究导致伸缩缝及其相邻路面损坏的车轮冲击荷载,以桥梁工程中常用的模数式伸缩缝为例,提出一种车辆-桥梁-模数式伸缩缝耦合振动的分析方法。该方法通过分布式弹簧阻尼单元模拟车轮在伸缩缝上的脱空情况;采用等效悬臂或两侧支撑梁模型,考虑脱空段轮胎面的支撑作用,通过车辆-桥梁-伸缩缝耦合振动的迭代算法,实现模数式伸缩缝上的车轮动力荷载的准确模拟,并对载重汽车通过双缝模数式伸缩缝进行实例分析。研究结果表明：①由于伸缩缝结构和车轮位置的变动,很难保证车辆振动的对称性,因此需要采用三维有限元方法分析车轮冲击荷载;②伸缩缝空隙处轮胎面的支撑有助于减小车轮冲击荷载,该支撑刚度与胎面预拉应力密切相关,胎面预拉应力越大,支撑刚度越大,轮载冲击系数越小;③车辆不对称振动导致左右轮冲击系数不同,模数式伸缩缝的中梁跨中冲击系数最大;④模数式伸缩缝上的轮载冲击系数计算值可能超过中国伸缩缝设计指南规定值,该方法可用于确定模数式伸缩缝的最大容许间隙,使车轮冲击荷载小于设计值,以保障伸缩缝的安全服役。     

Chaotic Motion of Wheels

Trolleys have wheels which can choose the direction of their rolling. Studying the motion of a wheel like this, we can often find periodic motions (“shimmy”) or even chaotic ones. It has also been experienced that the chaotic motions sometimes disappear quite unexpectedly. A strongly simplified model of these systems is analysed in the paper by means of the methods of bifurcation theory. Analytical and numerical results are shown to characterize the system, including simulation results. Similar behaviour can be found in more complicated systems as well, like the trailers or the nose-gears of aeroplanes. The development of the so-called transient chaotic motion is explained in these systems.     

Interaction Dynamics Between an Electric Vehicle's 'Pantograph' and the Road

In this paper, we briefly describe the patented E-TRAN electric roadway & vehicle concept and then proceed to study the dynamic effects of an associated road pantograph in contact with a road mounted power strip. During usage, the road pantograph (supported underneath the vehicle) allows power to be drawn from the strip for powering the motor driven vehicle. From a mechanical point of view, friction, wear and dynamic bounce effects impact the reliability arid maintainability of the pantograph/strip concept. To study bounce effects, a dynamic model of a one degree of freedom road pantograph was developed for both contact and noncontact situations. These dynamic “bounce” effects were simulated using a MATRIXx™ based model of the road pantograph and associated road surface (and strip). In order to do so, several simulation issues had to be addressed (some of which may be of interest to those studying wheel/rail contact effects). To corroborate the dynamic model, an instrumented experimental pantograph/road simulator was fabricated. Reasonable correspondence was achieved between the experimentally measured and simulated support forces and pantograph angle. Parametric variations in the design were also studied through simulation. The work presented serves as a paradigm for designing, building, and testing road pantographs for specific applications.     

Design of an Active Unilateral Brake Control System for Five-Axle Tractor-Semitrailer Based on Sensitivity Analysis

This paper presents the results of a parametric sensitivity analysis of a five-axle tractor-semitrailer vehicle combination using 3-DOF linear yaw/plane model. The first order logarithmic sensitivity functions are derived with respect to several vehicle design parameters. For stabilization of the vehicle's directional behaviour a fairly new control concept called “Active Unilateral Braking Control (AUBC)” acting on the tractor rear wheel's in order to produce a stabilizing yaw torque is investigated. The AUBC system improves not only the directional stability, but also affects the roll dynamics of the vehicle. The sensitivity of the controlled vehicle system with linear quadratic controller (LQR) is also examined, a robust controller design procedure is proposed as a result of the sensitivity analysis. The robustness of this controller in the presence of both internal (including parametric uncertainties, non-linear dynamics) and external disturbances (such as road irregularities and side wind) allows its implementation with confidence with a non-linear vehicle model. The applicability of this control system to a non-linear vehicle model is tested using a 34 DOF, non-linear vehicle model of the tractor-semitrailer combination.     

Optimales Abbremsen eines Fahrzeuges bei Kurvenfahrt

The problem of minimizing the stopping distance of a vehicle along a given trajectory is considered. A simple “one-wheel-model” for the vehicle and a suitable performance index for the optimization problem are derived. A simplified problem is considered first from which an analytical solution for the optimal trajectory is obtained. The suboptimal open loop control inputs are then approximately computed via a search algorithm. The results show that the performance nearly matches the predicted value.     

Application of Nonlinear Control Theory to Electronically Controlled Suspensions

This paper illustrates the use of nonlinear control theory for designing electro-hydraulic active suspensions. A nonlinear, “sliding” control law is developed and compared with the linear control of a quarter-car active suspension system acting under the effects of coulomb friction. A comparison will also be made with a passive quarter-car suspension system. Simulation and experimental results show that nonlinear control performs better than PID control and improves the ride quality compared to a passive suspension.     

盾构施工影响下砂土地层变形规律模型试验研究

为了研究盾构施工影响下隧道埋深、地层损失率、颗粒级配对砂土地层变形规律的影响,设计由试验模型箱、隧道开挖模拟装置以及非接触试验监测系统组成的模型试验系统,利用该试验系统对10种试验工况进行研究.试验模型箱是由钢化玻璃板、底部钢板以及刚框架组合而成的开口箱体,砂性地层采用完全烘干的砂土来制作,盾构开挖过程通过一种能够精确...