The design of a hold-off device to improve the lateral comfort of rail vehicles

ABSTRACT

Rail vehicles negotiating curves or in crosswinds are subjected to high lateral forces which provoke high displacements of the lateral suspension. As these displacements need to be limited due to gauging restrictions these forces cause the lateral suspension to reach the bumpstops and consequently the passenger comfort is significantly jeopardized. The paper presents the design of a pneumatic system that allows limiting the lateral displacement during curve negotiation (hold-off device). It describes the different phases of the design process starting from the definition of requirements to be fulfilled. The main components and the effect of their characteristics on the overall performance of the centring system are studied, and completed with an experimental analysis of the centring system. Finally, the described methodology is applied to a typical high speed rail vehicle. The results prove that the concept of a centring system which uses the same technology and components that are used in rail vehicles for the pneumatic height control system of secondary suspensions is possible. This fact is particularly interesting as the market offers this kind of components and has proven their reliability during many hours of service therefore the new hold-off system will be based on in-service validated components.     

Simulation of Dynamical Behaviour of a Front Wheel Suspension

A MacPherson front wheel suspension and its components are modelled with the finite element method. Nonlinearities due to both the geometry and the characteristics of the components (springs, dampers and bushings) are considered. The force due to a given compression/elongation of the spring strut is calculated and compared with experimental results. Kinematical results, change in track width and camber angle, are also shown and compared with experimental results. Good agreement between numerical and experimental results is obtained.     

A Comparison of Various Computer Simulation Models for Predicting the Directional Responses of Articulated Vehicles

SUMMARY

This paper presents the results of a comparative study of the predictions, made using computer simulation models of different levels of complexity, of the directional responses of commercial articulated vehicles in steady-state and lane-change maneuvers. The differences in the predictions obtained using various models are examined and are compared with available experimental data. The objective of this study is to compare the capabilities and limitations of various simulation models for predicting the directional behavior of articulated vehicles.     

Numerical Simulation and Experimental Verification of the German Roller Rig for Rail Vehicles*

SUMMARY

A numerical simulation model of the roller test stand located at Munich and loaded by a bogie is discussed including its technical structure, the governing physical equations of motion and the structure of the simulation program.

Both, the set up of the mathematical and numerical models time and the computation time of simulation runs have been considerably reduced (by a factor of 20) using formula manipulation programs.

Simulation results concerning the

• starting behaviour of a bogie,

• stationary limit cycle behaviour of bogies with ideal and wear profile and

• influence of gauge changes and spring/damper modifications on limit cycle behaviour of a bogie are presented, some of which are compared with experimental results gained from test facility measurements. The simulation results are in good agreement with the experimental results and provide an experimental verification of the roller rig simulation model presented.

     

Application of Nonlinear Control Theory to Electronically Controlled Suspensions

SUMMARY

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.     

Dynamic Response of a Six-axle Locomotive to Random Track Inputs

SUMMARY

Spectral analysis techniques are employed to analyze the dynamic response of a six-axle locomotive on tangent track to vertical and lateral random track irregularities. The locomotive is represented by a thirty-nine (39) degrees of freedom model. A linear model is employed by considering small displacements, linear suspension elements and a linear theory for the wheel-rail interaction. Power spectral densities of displacements, velocities and accelerations and the statistical average frequencies of the system are obtained for each degree of freedom. Comparison of the calculated dominating frequencies with existing experimental values shows good agreement. The technique of spectral analysis is an effective tool for model validation, and for the determination of rail vehicle response to track irregularities. The probability functions for the response can be used as a measure for the ride quality of rail vehicles and for the study of fatigue damage of components.

     

Simulation Approach to the Effect of the Ratio Changing Speed of a Metal V-Belt CVT on the Vehicle Response

SUMMARY

In regard to the belt and pulley system of a metal V-belt CVT, the characteristics of the ratio changing speed is obtained by experiments. It is summarized in a practical and simple experimental equation. By using this equation a simulation model is developed to analyze the response of a vehicle with a metal V-belt CVT to a rapid pulley ratio change. The simulation results are in reasonable agreements with experimental results.     

Aerodynamics of Road- and Rail Vehicles

SUMMARY

The technical state-of-the-art of aerodynamics of ground transportation vehicles is reviewed. Currently available theoretical calculation methods and experimental simulation techniques as well as typical results illustrating the impact of aerodynamics on vehicle performance and running characteristics are summarized and the interactions between vehicle system dynamics and aerodynamics are adressed. Correlation of theoretical and experimental data show the present potential of vehicle aerodynamics and point to fields in which further research work is necessary.     

Road roughness estimation based on discrete Kalman filter with unknown input

ABSTRACT

The road roughness acts as a disturbance input to the vehicle dynamics, and causes undesirable vibrations associated with the ride and handing characteristics. Furthermore, the accurate measurement of road roughness plays a key role in better understanding a vehicle dynamic behaviour and active suspension control systems. However, the direct measurement by laser profilometer or other distance sensors are not trivial due to technical and economic issues. This study proposes a new road roughness estimation method by using the discrete Kalman filter with unknown input (DKF-UI). This algorithm is built on a quarter-car model and uses the measurements of the wheel stroke (suspension deflection), and the acceleration of the sprung mass and unsprung mass. The estimation results are compared to the measurements by laser profilometer in-vehicle test.     

Vergleich einiger Rechen- und Messergebnisse zum Fahrverhalten von Sattelzügen

SUMMARY

In this paper some results of theoretical and experimental investigations on the dynamic directional properties of heavy tractor-semitrailer vehicles are presented.

A nonlinear digital computer model was developed on which the theoretical system analysis is based. This model takes account of the nonUnear tire properties and the friction couple of the fifth wheel. A combination of numerical computation methods (Runge-Kutta and Newton-Raphson techniques) is used for the digital computer simulation.

Full scale road tests with articulated vehicles of 38 ton total weight were conducted for experimental validation of the used theoretical model. As input signals to the vehicle, predetermined steering wheel angle functions were used. The system output signals corresponding to these input functions were measured and stored.

A comparison of the obtained theoretical and experimental results shows a very good qualitative agreement and hence leads to the conclusion that the developed theoretical model can give consistent estimates of the basic dynamic vehicle properties.     

DISCUSSION NOTE on Karnopp's article “Active Damping in Road Vehicle Suspension Systems”

SUMMARY

In this paper, an optimal suspension system is derived for a quarter-car model using multivariable integral control. The suspension system features two parts. The first part is an integral control acting on suspension deflection to ensure zero steady-sate offset due to body and maneuvering forces as well as road inputs. The second is a proportional control operating on the vehicle system states for vibration control and performance improvement. The optimal ride performance of the active suspensions based on linear full-state feedback control laws with and without integral control together with the performance of passive suspensions are compared.     

Stability Analysis of Constant Speed Transit Vehicles On Straight,Horizontal, Fixed Guideways

SUMMARY

Several methods of motion stability analysis are examined and compared in the context of the problem posed by a simple idealization of a transit vehicle moving at constant speed on a straight, horizontal, fixed guideway, supported by idealized rubber tires, air cushion pads, or semiconical steel wheels on steel rails. Stability analysis methods examined include Liapunov analysis with the Hamiltonian and with a modified Hamiltonian proposed by Walker, and analysis of characteristic equations using theorems due to Routh, Hurwitz, Cronin, and Liénard and Chipart It is concluded that for rubber-tired and aircushioned vehicles a Liapunov analysis employing the Hamiltonian is most efficient, and for the tracked vehicle the criteria of Liénard and Chipart are most useful.     

Improvement of Vehicle Dynamics by Rear Braking Force Control

SUMMARY

A study on effective use of rear braking force to improve a brake performance and vehicle dynamics are carried out. On a ordinary condition, the rear braking force could be more increased to a conventional braking force distribution. Based on this thought, the brake performances are estimated. The results show the effects not only improve the brake performance but also reduce a pitching at braking and moderate a vehicle OS behavior in a turn during braking. These are verified by experimental test vehicle equipped with a rear braking force control system.     

Dynamic Interaction of Railway Systems with Large Bridges

SUMMARY

In this paper have been described

- railway runability problems on large span bridges;

- the state-of-art of the methodologies adopted for a systematic analysis of the dynamic behaviour of railway vehicles running on a deformable structure, with particular reference to large span suspension bridges;

- some meaningful experimental and analytical results, related to railway runability of large span bridges.     

Analysis of Automatic Steering Control for Highway Vehicles with Look-down Lateral Reference Systems

SUMMARY

In this paper, steering control for passenger cars on automated highways is analyzed, concentrating on look-down reference systems. Extension of earlier experimental results for low speed to highway speed is shown to be non-trivial. The limitations of pure output-feedback of lateral vehicle displacement from the road reference are examined under practical constraints and performance requirements like robustness, maximum lateral error and comfort. The in-depth system analysis directly leads to a new alternative design direction which allows to preserve look-ahead reference systems for highway speed automatic driving.     

A Modular Computer Model for the Design of Vehicle Dynamics Control Systems1

SUMMARY

This paper describes a multiport approach to computer-aided modeling of vehicle dynamics. The modeling approach produces models that are suitable for the interactive design and evaluation of complex control strategies. The vehicle model which can be used for ride and handling analysis, is built from modular components. The components are programmed using the syntax of the computer aided control system design (CACSD) program EASYS. Seven modeling components are used to create a three-dimensional vehicle dvnamics model. The model is flexible enoug-h to simulate any suspension design with revolute joints.

Each component of the model consists of a FORTRAN subroutine and a main calling module called a macro. To simplify the process of model building, the modeling components in the car model are designed to represent physical elements, such as the spring, damper, link or tire. To create a model, the components, which are represented by blocks, are interconnected through points, located on the blocks, called pons. These ports have been designed to simulate the location of the connection points between the physical elements, as observed in real systems. The construction of multibody models within a CACSD program offers the flexibility of simultaneous interactive simulation of the three-dimensional dvnamics and evaluation of the desien of the controls.

Although modeling of multibody systems using FORTRAN components has been pioneered by Chace, Haug and Orlandea; and bond graph modeling of multibody systems has been investigated by Bos, this approach is novel because:-

The model is included in the control system design program (EASYS). This arrangement allows the designer to exploit the advanced control design tools available in the program. Furthermore, this approach significantly reduces the computation time required for running the model after parameters modification.

The model is built from components that are interconnected by ports which represent the actual physical location of the connection points between the elements. The multiport approach simplifies the model building process for multibody systems. This simplification is achieved by reducing the model of a multibody system to a block diagram form.     

Power Requirement of Active Vibration Control Systems

SUMMARY

The paper deals with the theoretical estimation of the minimal power requirement, necessary for the operation of the active vibration control system (AVCS), connected with a passive one. It is assumed this compound system is used for the vibration control purposes in the heavy vehicle driver's seats. The systems considered in the paper are of two kinds. In the first case the electro-hydraulic actuator of the AVCS is situated in series to the spring-damper combination of the seat suspension. The second system under consideration is formed by parallel connection of electro-pneumatic actuator and the spring-damper combination of the seat suspension, which is a mechanical model of a real air spring with controlled in-flow and out-flow of the air. The comparison of results for both compound systems shows markedly higher power consumption of the serial system. The theoretical results are in acceptable agreement with the experimental data.     

On model-based longitudinal feed-forward motion control for low velocities on known road profiles

ABSTRACT

So far, longitudinal motion control has focused on situations like highway driving, where disturbances of the road profile can be neglected. In this paper, we show how the Two Point Tire Model can be used to derive a novel feed-forward control law for a vehicle's longitudinal motion that considers the effects of the road profile and can complement existing control approaches. For this purpose, we recapitulate the basic model assumptions and equations and briefly discuss how it can be used on arbitrary road profiles. Two approaches for implementation in a real vehicle are presented. Comparisons of these approaches in simulation and to a human driver of an experimental vehicle show that the controller can deal with stepped obstacles of up to 14?cm in height. However, the control performance is essentially limited by the actuator delay and human drivers outperform the controller due to their ability of sensing subtle vehicle motions. The results indicate that the control performance can be further improved by using a preview on the necessary drive torque, which can be provided by the solution that we propose.     

Comparison of Ride Comfort Criteria for Computer Optimization of Vehicles Travelling on Randomly Profiled Roads

SUMMARY

This paper discusses and compares some ride comfort criteria which may be suitable for randomly vibrating vehicles. The criteria consider single-figure measures based on response mean square spectral densities for plane linear combined vehicle-passenger models. Eight different measures divided into three groups are studied. The two vehicle suspension damper stiffnesses are numerically optimized with respect to the eight measures of ride comfort. The results are compared and discussed. Two optimizations with respect to five vehicle parameters are also reported.