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244 1. Conventional Autocouplers and Draft Gear Packages Aconventional autocoupler and draft gear package is illustrated in the schematic in Figure 9.2. Aschematic of the wedge arrangement of the draft gear unit is includedinFigure 9.3.Variations on the arrangement showninFigure9.3 exist. Some designs include an additional taper in the housing or are provided by additional wedges as shown in Figure 9.4. The stick–slip nature of the friction wedges has also led to recent innovations such as those showninFigure 9.5,which include arelease spring. In adesign of this type, the release spring is provided to unlock the outside wedge thereby releasing the friction wedges. When considering awagon connection, two autocoupler assemblies must beconsidered along with gap elements, and also stiffness elements describing flexure in the wagon body. Awagon connection model will therefore appear assomething similar to the schematic inFigure 9.6. Modelling the coupler slack is straightforward, a simple dead zone. Modelling of the steel components including wagon body stiffness can be provided by asingle linear stiffness. Work by Duncan and Webb 1 from test data measured on long unit trains identified cases where the draft gear wedges locked and slow sinusoidal vibration was observed. The behaviour was observed in distributed power trains when the train was in asingle stress state. The train could beeither in atensile or compressed condition. The stiffness corresponding to the fundamental vibration mode observed was defined as the locked stiffness ofthe wagon connections. The locked stiffness value for the trains tested, (consisting of 102 coal hopper cars each of 80 tonne gross mass), was nominally in the order of 80 MN/m. 1 As the locked stiffness isthe limiting stiffness ofthe system, it must be incorporated into the wagon connection model. The locked stiffness is the sum of all the stiffness’ added in series,which includesthe components such as the coupler shank, knuckle, yoke, locked draft gear, and wagon body. It also includes any pseudo-linear stiffness due to gravity and bogie steer force components, whereby alongitudinal force is resisted by gravity as awagon is lifted or forced higher onacurve. The limiting stiffness ofalong train may therefore vary for different wagon loadings and on-track placement. Wagon connection modelling can be simplified to acombined draft gear package model equivalent to two draft gear units and includes one spring element representing locked or limiting stiffness, Figure 9.7. Yoke Wagon Body Draft Gear Unit FIGURE 9.2 Conventional autocoupler assembly. Polymer Spring or Steel Coil Spring FIGURE 9.3 Friction type draft gear unit. © 2006 by Taylor & Francis Group, LLC Handbook of Railway Vehicle Dynamics Coupler Shank Friction Wedges Rod Knuckle
Longitudinal Train Dynamics 245 Polymer Spring or Steel Coil Spring Surface Angle Shown Larger than Actual FIGURE 9.4 Friction type draft gear unit with angled surfaces. Friction Wedges Determination of the mathematical model for the draft gear model has received considerable attention in technical papers. For the purposes of providing amodel for train simulation, apiecewise linear model representing the hysteresis in the draft gear friction wedge (or clutch) mechanism is usually used. 1,9 The problem of modelling the draft gear package has been approached in several Rod Steel Coil Spring Friction Wedges Release Spring FIGURE 9.5 Friction type draft gear with release spring. Stiffness :Wagon Body and Draft Gear Mounting Draft Gear Model Stiffness :Coupler Shank, Knuckle,Yoke FIGURE 9.6 Components in awagon connection model. Combined Draft Gear Model Limiting Stiffness or 'locked stiffness' FIGURE 9.7 Simplified wagon connection model. © 2006 by Taylor & Francis Group, LLC Outside Wedge Release Rod Stiffness :Wagon Body and Draft Gear Mounting Coupler Slack Coupler Slack Draft Gear Model
Page 1 and 2: 9 CONTENTS Longitudinal Train Dynam
Page 3 and 4: Longitudinal Train Dynamics 241 ass
Page 5: Longitudinal Train Dynamics 243 By
Page 9 and 10: Longitudinal Train Dynamics 247 For
Page 11 and 12: Longitudinal Train Dynamics 249 If
Page 13 and 14: Longitudinal Train Dynamics 251 var
Page 15 and 16: Longitudinal Train Dynamics 253 For
Page 17 and 18: Longitudinal Train Dynamics 255 Com
Page 19 and 20: Longitudinal Train Dynamics 257 Tra
Page 21 and 22: Longitudinal Train Dynamics 259 Bra
Page 23 and 24: Longitudinal Train Dynamics 261 The
Page 25 and 26: Longitudinal Train Dynamics 263 G .
Page 27 and 28: Longitudinal Train Dynamics 265 Lon
Page 29 and 30: Longitudinal Train Dynamics 267 FIG
Page 31 and 32: Longitudinal Train Dynamics 269 tak
Page 33 and 34: Longitudinal Train Dynamics 271 “
Page 35 and 36: Longitudinal Train Dynamics 273 Res
Page 37 and 38: Longitudinal Train Dynamics 275 ope
Page 39: Longitudinal Train Dynamics 277 V f

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