Active Yaw Relaxation For Improved Bogie Performance

SUMMARY

The use of controlled traction rods to give active yaw relaxation of coned wheelsets is investigated, and is shown to give significant improvements in curving performance without compromising stability, even on curves for which there is flange contact. An assessment of practical implications such as power, actuator and control requirements is included.     

Stability Criteria for Articulated Railway Vehicles Possessing Perfect Steering

SUMMARY

The general form of the equations o f motion o f multi-body articulated railway vehicles are used to establish the conditions which the elastic stiffness matrix, which describes the nature and configuration o f the suspension elements connecting the various bodies, must satisfy in order to achieve both perfect steering on circular curves and dynamic stability. The resulting criteria are then used to discuss the properties of various multi-axle configurations which are either typical of current practice or possibilities for future designs.     

Forced Steering of Rail Vehicles: Stability and Curving Mechanics

SUMMARY

A forced steering rail vehicle employs linkages between.the carbody and wheelsets to force a more radial wheelset alignment. It is shown that the curve negotiation capability of forced steering trucks is significantly improved over conventional and self steering radial trucks. Parametric curves are presented showing angle-of-attack and lateral flange force as a function of steering gain parameters and truck bending stiffness. It is also shown that the forced steering concept can produce kinematic instability and severely reduced critical speeds for low conicities and creep coefficients. Analytic expressions are derived that illustrate how these kinematic instabilities can be avoided.     

Semi-Active Attitude and Vibration Control

SUMMARY

The paper discusses the attitude and vibration control of a passenger car on the basis of a full vehicle model. The analysis presented consists of two parts: (I) The introduction of a newly developed semi-active anti-roll/pitch system, (ii) An example of an actively suspended full vehicle model using a simple control strategy to improve ride comfort. The attitude control using semi-actively generated compensation forces prevents the car from rolling in curves and pitching during braking or accelerating. The strength of the system is the small energy consumption. The performance of the combination of both attitude and vibration control can compete with a fully active suspension system.     

Railway Vehicles With Generic Bogies Capable of Perfect Steering

SUMMARY

The general form of the equations of motion of a symmetric railway vehicle with two unsymmetric two-axle bogies is derived. The equations include a generic elastic stiffness matrix that describes the nature and configuration of the structural connections between the various components of the vehicle. This matrix satisfies the condition for perfect steering (without generating creep forces) on uniform curves and the necessary condition for dynamic stability derived in previous work. The paper shows the application of these basic conditions to a class of generic unsymmetric bogies. The analysis has as its objective the derivation of the simplest rather than the most general configuration that meets the conditions imposed. The results are related to past and current practice. It is shown that perfect steering, with stability at low speeds, can be achieved by means of passive suspension elements not employing linkages, and that it is possible to simplify existing steering arrangements.     

Energy Dissipation Due to Vehicle/Track Interaction

SUMMARY

The effects of track irregularities and wheel profile on the amount of energy dissipated in railroad freight vehicles is examined. A nonlinear computational model is used to determine the average dissipation in the vehicle suspension and the wheel/rail contact patches. This dissipation is a component of the total resistance force acting on the vehicle. Parametric results are presented showing the effects of track geometry, wheel profile, suspension design, and hunting on train resistance. Track geometry studies consider the effects of track quality and curving. The AAR 1:20 wheel profile and the Heumann wheel profile are compared under various operating conditions. Compared with the Heumann profile, the AAR 1:20 profile is shown to have lower average resistance on good quality tangent track, but higher average resistance in steady curves. A trade-off exists between the two profiles when dynamic curve entry is considered.     

Dynamic Behaviour of Ore Wagons in Curves at Malmbanan

SUMMARY

The transportation of ore can be made more cost efficient by use of bigger and heavier trains. An increase in axle load is thereby wanted. The fleet of ore wagons of today at Malmbanan/Ofotbanan in northern Sweden and Norway has to be updated. It is of interest to find out if it is possible to allow a higher axle load on the track with new wagons

To be able to understand and predict the effects on track wear depending on what type of vehicle that is in use, the contact forces between wheels and rails have to be determined. A computer aided analysis has been made of the dynamic behaviour of three test vehicles equipped with different types of three-piece bogies running at Malmbanan. The vehicles are modelled and their interaction with the track is analysed using the multibody simulation package GENSYS

The simulations show that, even if the axle load is increased from 25 tons to 30 tons and the velocity is increased from 50 km/h to 60 km/h, it is possible to reduce lateral track forces and wear in curves by using a different bogie than the standard three-piece bogie used today.     

Computer-Aided Analysis of Urban Railway Vehicles

SUMMARY

Computer-aided dynamic simulations are usually employed when designing modern urban railway vehicles. Even if the modeling procedure is similar to the one used for trains, specific features have to be taken into account for tramways: they are designed for low speeds (less than 80 km/h) and narrow curves (less than 20 m of radius). Moreover, in order to improve accessibility, low floor designs have been developed (the floor lying at about 300 mm above the rails level). The simulation procedure has therefore to take account of the occurence of multiple wheel/rail contacts or the modelization of independent wheels. A specific software well adapted to the computer-aided design of urban railway vehicles has been developed by the Faculte Polytechnique de Mons. It performs the following classical analyses:

lateral linearization, modal analysis and root locii plots;

vertical linearization and comfort prediction;

non-linear time simulation in straight track (limit cycles) and in curve (derailment study)

parametric analyses

The vehicle model is formed by combination of bodies ( or flexible bodies, rotating bodies like wheelsets or independent wheels) and interconnection elements ( spring and damper elements). Contact between rails and wheels is treated as a part of the rotating bodies. A residual formulation has been preferred. When combined with the use of a complete iteration matrix, this formulation is well adapted to the treatment of stiff differential equations. It is based on a fast determination of the residues of the dynamic equations combined with the calculation of the iteration matrix through a numerical derivation procedure. The advantages of the approach are discussed. The model of a partial low floor vehicle with wheelsets and independent wheels is described.     

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.     

Effect of Frame Compliance on the Lateral Dynamics of Motorcycles

SUMMARY

The lateral dynamics of an uncontrolled motorcycle, running on a straight, level road surface, is investigated in this paper. The structural compliances in the front and the rear frames of the motorcycle are taken into account by introducing additional degrees of freedom in the analysis. The kinematics of the tires is represented by linear differential equations which are based on the taut-string model of pneumatic tires. The linear differential equations of motion are solved to yield the eigensolutions of the system. Numerical results, obtained for parameters corresponding to a Honda CB750 motorcycle, are presented and discussed.     

Optimal Control of the Tractor-Semitrailer Truck

SUMMARY

This paper is concerned with the braking performance and the handling behavior of the tractor-semitrailer truck under optimal braking. Optimal control theory is used in order to deal with the problem and a combination of the steepest descent method and the Davidon Fletcher Powell method is used to solve it numerically. Results for some chosen braking maneuvers are obtained for a nonlinear truck model which has 14 degrees of freedom. These results show that, for the chosen maneuvers an idealized anti-skid braking is close to being optimal in the sense defined in this paper. Implementation of an idealized anti-skid braking on the tractor-semitrailer truck, however, may be not desirable.     

Evaluation of transportation alternatives for aging population in the era of self-driving vehicles

ObjectiveAccess to transportation is very important for older adults as it allows them to lead an independent and social life. With a growing elderly population, providing access to transportation is one of the greatest societal challenges in the United States. A feasible solution to this problem is adoption of self-driving vehicles in order to provide safe, convenient, and affordable transportation services to older adults. This study analyzed older adults' acceptance of three transportation alternatives that utilize self-driving vehicles. In addition, older adults' travel behavior and transportation needs were also assessed.MethodsAn online survey approach was adopted to collect data on older adults' travel behavior, transportation needs, and to evaluate three transportation alternatives. The three self-driving transportation alternatives presented were owning a self-driving vehicle, using prepaid taxi services, and getting rides through community services. A total of 173 survey responses were collected from participants aged 60 years or older.ResultsParticipants (80% or more) responded that they are satisfied with the number of trips they make to stores, medical centers, and to religious and social events. On the other hand, more than one-third of the participants would make more trips than they currently do to visit family and friends and to recreational places if rides were available. Among the three alternatives, prepaid taxi services received the best overall ratings. A majority of the participants also responded that owning a self-driving vehicle was not affordable to them.ConclusionsThis study provides valuable information that could be used to design future transportation services for the elderly population. Older adults are willing to adopt self-driving vehicles as a mode of transportation. However, automakers and federal authorities need to make efforts to inform older adults about the benefits of these vehicles, and their safety features.     

Berechnung des extremen Lenk- und Bremsverhaltens von Sattelkraftfahrzeugen

SUMMARY

Simulation of Steering and Braking Behaviour of Tractor-Semitrailer Vehicles in Extreme Situations

This paper deals with the simulation of the behaviour of tractor-semitrailer vehicles at braking on wet, slippery road surface. The nonlinear model used for the computation enables to simulate extreme situations at wheel locking and swerving

The instabilities during braking such as jackknifing and trailer swing as well as non steerability are investigated. Straightline braking shows the influence of cornering on the behaviour during braking in a turn.     

The effect of motorcycle safety campaign on helmet use: A systematic review and meta-analysis

ObjectiveThis systematic review and meta-analysis was undertaken to estimate the effectiveness of motorcycle safety campaigns for increasing helmet use among motorcycle riders and passengers.MethodsPubMed, Scopus, EMBASE, and the Web of Science (WOS) databases were systematically searched up June 2020 for all relevant studies. The National Institute of Health (NIH) tool was used to assess the quality of all included studies. Inter-study heterogeneity was measured using the Chi-Squared and I² statistics, with the odds ratio (OR) being used as a measure of the pooled effect size.ResultsOut of the 561 records identified from the literature searches, eight articles (or 11 studies) were eligible for inclusion in the present meta-analysis. Using a random effects model, the results of the meta-analysis demonstrated statistically significant increases in helmet use among motorcycle riders (OR = 4.52, 95% CI: 1.01–20.14, I² = 99.9%) and passengers (OR = 6.57, 95% CI: 1.41–30.56, I² = 99.9%). The findings of sensitivity analyses, based on alternative levels of r for imputing the standard error (SE) of the ORs, showed the pooled OR of helmet use among motorcycle riders (r = 0.7; 3.49; 95% CI: 0.78, 16.44; r = 0.9; 3.49; 95% CI: 0.76, 16.11) was sensitive to different levels of r. However, no significant effect was detected on the pooled effect size for different correlation coefficients for motorcycle passengers (r = 0.7; 6.56; 95% CI: 1.59, 27.00; r = 0.9; 6.56; 95% CI: 2.25, 19.13). Increases in helmet use among motorcycle passengers were found in studies that: monitored pre and post campaign periods for longer than one year and were conducted in Thailand or Vietnam. However, the effect of motorcycle safety campaigns on helmet use among motorcycle riders remained significant for all of the different strata included.ConclusionThe present meta-analysis found that motorcycle safety campaigns can lead to a significant increase in helmet use among both motorcycle riders and passengers. Due to the high degree of inter study heterogeneity, these findings should be interpreted with some caution. Despite the apparent favourable influence of motorcycle safety campaigns, more robust research is required.     

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.     

Optimal Design of Running Gears Part II. Applications

SUMMARY

In the second part of the paper applications are shown for the two-axle unsymmetric running gear and for symmetric running gears with two, three and four wheelsets.     

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.