Interface - The Journal of Wheel/Rail Interaction

FLANGE CLIMB

Flange Climb and Independently Rotating Wheels
(continued)

Simulated comparisons
Using NUCARS™ (New and Untried Car Analytic Regime Simulation), researchers at the Transportation Technology Center, Inc., looked at the effect of IRWs on flange climb under two representative LRVs. LRV1 included two articulated car bodies with three trucks (one beneath the articulation joint). LRV2 included three articulated car bodies with a center truck under the middle of the shorter center car body—a common low-floor arrangement. Performance of the vehicles, which used the same wheel (and rail) profiles, was modeled entering a 5-degree curve with 2 inches of superelevation with combined crosslevel, lateral alignment and gauge deviations in the body of the curve. Both vehicles were simulated with conventional rigid axle wheelsets on all three trucks, and with IRWs on the center truck.

While both types of wheelsets see the same external lateral and vertical forces, and both types generate lateral creep forces relating to angle of attack, only the conventional rigid-axle wheelsets generate longitudinal creep forces and, therefore, a yaw (steering) moment.

IRWs, on the other hand, generate no longitudinal forces and, therefore, no yaw, or steering, moment. While this produces a vehicle that will not hunt, it destroys the feedback mechanism that enables the wheelsets to self-steer. As a result, trucks with IRWs tend to operate with higher angles of attack, with no longitudinal force to assist in reducing the lateral flange climbing force. "This results in much shorter wheel climb distances," Elkins said.

Figure 1 (on preceeding page) shows the distance it takes the flanging wheel of a conventional wheelset (left) to climb as a function of angle of attack and the COF on the non-flanging wheel. The Figure shows that the IRW behavior is similar to a conventional wheelset with very low friction on the non-flanging wheel. It also indicates that the distance to climb for the IRW is unaffected by the COF on the non-flanging wheel—even at very high friction levels.

"The lower the COF on the non-flanging wheel, the more the rigid axle behaves like an IRW set," Elkins said. The reason for this is that if the COF on the non-flanging wheel is reduced to almost nothing, the longitudinal force on that wheel is destroyed. The absence of a longitudinal force on the flanging wheel is a primary reason why an independently rotating wheel is more likely to derail, he said.

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