Dynamics of Railway Wagons Subjected to Braking/Traction Torque

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Dynamics of railway wagons subjected to
braking/traction torque
Downloaded By: [Queensland University of Technology] At: 00:16 10 September 2008

Zuoyan Zhanga and Manicka Dhanasekarb *
a Centre

for Railway Engineering, Central Queensland University, Queensland, Australia; b Faculty of Built Environment and Engineering, Queensland University of Technology, Brisbane, Australia (Received 20 October 2007; final version received 24 February 2008 ) Braking or traction torque is regarded as an important source of wheelset skid and a potential source of derailment risk that adversely affects the safety levels of train operations; therefore, this research examines the effect of braking/traction torque to the longitudinal and lateral dynamics of wagons. This paper reports how train operations safety could be adversely affected due to various braking strategies. Sensitivity of wagon dynamics to braking severity is illustrated through numerical examples. The influence of wheel/rail interface friction coefficient and the effects of two types of track geometry defects on wheel unloading ratio and wagon pitch are also discussed in the paper.

Keywords: braking/traction torque; derailment potential; wheel unloading; wheelset skid; track irregularity; wagon pitch

1.

Introduction

Braking and traction torques are not explicitly considered in most of the wagon dynamics simulation packages, as their primary focus is to provide a platform for long-distance route simulations with near-real-time scenarios which demand fast-solution algorithms. These packages consider the braking scenarios through the definition of speed profile as a priori. It is commonly acknowledged that the speed profile is affected by tribological and geometric parameters at the wheel/rail interface and the characteristics of brake application. Furthermore, other parameters, especially the primary and secondary suspension responses, are also sensitive to the resulting speed profile. It is shown in [1] that a fixed coordinate system is essential to calculate the speed profile from brake torque input. Hence, it is prudent to evaluate the speed profile based on input torque due to traction/brake forces; this research has considered such an approach. The wagon response due to brake torque could be either stable or unstable depending on the brake torque history, the friction characteristics and the wagon parameters. The pneumatic (air) brake that is commonly used in freight trains provides a continuous and large braking torque to all wheels. The brake torque produces profound effects on the wheel–rail contact characteristics and hence has the potential to affect the stability of wagons. Qian and Chen [2] have described the threedimensional dynamic response of wagons during normal braking mode. Severe braking has been *Corresponding author. Email: m.dhanasekar@qut.edu.au

ISSN 0042-3114 print/ISSN 1744-5159 online
© 2008 Taylor & Francis
DOI: 10.1080/00423110802008124
http://www.informaworld.com

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Z. Zhang and M. Dhanasekar

Downloaded By: [Queensland University of Technology] At: 00:16 10 September 2008

shown to cause wheelset locking and skidding that could potentially damage the wheels (wheel flat) and the railhead (engine burn) in addition to the potential for the derailment of the wagon itself. Handoko and Dhanasekar [3,4] simulated bogies subjected to heavy braking torques; wheelset skid and bogie pitch are described in their paper. Track geometry defects induce diverse effects on wagon dynamics as reported in Chen and Jin [5]. A generalised formulation to incorporate track irregularities to railway dynamics was presented by Yang [6]. Emergency braking and full ordinary braking under poor rail/wheel friction conditions are shown to cause 30% of derailments in Russia [7]. The effect of track geometry defects in addition to the sensitivity during braking or traction state is also presented in the current paper.

2. Wagon braking and traction systems and...
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