Interface - The Journal of Wheel/Rail Interaction

VEHICLE TESTING

Testing Railway Vehicles to Improve Vehicle/Track Interaction (continued)

Derailment potential on twisted track
The tests are intended to ensure that vehicles can run safely on twisted track. Track twist is a result of transition layout between level and canted track, as well as crosslevel deviations (maintenance limits). This test must be completed for initial acceptance of all vehicles. For the extension of acceptance the test must be repeated if the variation of parameters increases the risk of derailment.

The limit value

for initiating flange climbing is influenced by the flange angle and the friction forces between flange and rail. These forces are determined by the characteristic of the surface of wheel and rail at the contact point and by the angle of attack between the wheel and rail.

For universal application there are two primary methods to prove safety against derailment: (1) Twisted test track. This includes measurement of the vehicle as it negotiates a twisted test track. (2) Twist test rig and flat test track. This includes: measurement of the minimum wheel force

on a vehicle test rig, measurement of the guiding force

on an appropriate test track, and calculation of the ratio

. Test methods 1 and 2 require the direct measurement of forces between wheel and rail.

A third method (3), Twist test rig and yaw test rig, is also possible. This method includes: measurement of the minimum wheel force

on a vehicle test rig, and measurement of wheel forces and the torque required to rotate (yaw) the bogie in a small radius curve.

Longitudinal forces
Longitudinal forces within trains have the potential to increase the risk of derailment when negotiating S-shaped curves. For conventional trains (except for freight) this risk is regarded as low. However, this risk must be considered when non-conventional configurations are in use. Tests to identify issues in this area are broken down into three categories: sway characteristics, rotational resistance, and static wheel force.

The sway characteristics test is intended to evaluate the vehicle body's displacement in the transverse and roll direction caused by a lateral acceleration (acting in track plane). The test may be necessary to validate vehicle data used to determine its kinematic envelope, and to determine the transverse movement of the pantograph (for a powered vehicle with overhead lines) to confirm that the risk of loss of contact between pantograph and contact wire is low.

The vehicle can either be tested on a special rig or on track. The test rig simulates canted track and measures the roll angle and transverse movement of the carbody, in order to provide a detailed analysis of the roll coefficient. The rig test allows for precise measurement of the sway characteristics (i.e. roll and transverse movements).

In on-track tests, measurements are taken of lateral accelerations in the vehicle body, cant deficiency in curves and roll angles in the suspension levels. On-track tests are limited to determination of the roll characteristics, and must be completed for certain vehicles by measurement and analysis of lateral movement between bogie and body.

The rotational resistance test is intended to evaluate body-to-bogie yaw torque. One application is the measurement of yaw torque, which is generated as the vehicle passes through curves, switches and crossings. The test may be carried out for the proof of safety against derailment.

Measurement of static wheel forces is intended to evaluate the vehicle's mass and the distribution of the wheel forces (wheel loads). This includes tests for vehicle mass, vertical force per axle, and vertical force per wheel. All new or modified vehicles must perform on-track tests with regard to their dynamic characteristics. This includes monitoring the vehicle under various operating conditions, including speed, curve radius and cant deficiency (see Table1 - click here.)

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