Keywords: track-friendliness, running stability, wheel wear, rail wear, simulations, on-track tests.

A railway wheelset with conical wheels has an inherent self-steering ability to align itself approximately radially in curves. By doing so, the creepage between wheels and rails as well as the resulting creep forces will usually be of modest magnitude, resulting in low energy dissipation and a modest wheel and rail wear. In reality, however, all wheelsets in a rail vehicle are guided in and connected to a bogie frame or to the main frame of the vehicle, which more or less restricts the steering ability. In order to allow radial self-steering, the longitudinal flexibility between wheelset and its surrounding frame is a most important issue.

A certain amount of stiffness in the wheelset guidance is necessary to avoid hunting, i.e. self-generated sustained lateral vibrations. The needs for longitudinal and also lateral stiffness normally increase at higher speeds and at higher conicity in the wheel-rail contact. However, a stiff wheelset guidance risks the deterioration of curving performance in terms of wheel and rail wear and lateral forces on the track. These properties are substantial parts of what is often called track friendliness of a rail vehicle.

A case study is presented where a "track-friendly" bogie is optimized to be able to run at speeds up to 250-300 km/h. The paper firstly discusses the optimization targets in general with respect to wear, critical speed and the above-mentioned considerations. Secondly, the paper describes a systematic optimization procedure involving the adequate parameters and conditions of importance to the targets.

A large number of simulations have been carried out with wheel-rail contact conditions that cover a large variety of conicities. Both straight track and large radius curves have been taken into account to optimize the hunting behaviour. Predicted curving and hunting performance is compared with measured data from the test train "Regina 250" in the "Green Train" programme. This train has been subjected to testing according to EN 14363 [1] at speeds up to about 300 km/h and in various curves with radii ranging from 250 m and up. The presented case shows the possibility of optimizing a vehicle for both high-speed stability under conditions of high and low equivalent conicity as well as for a modest wheel and rail wear.

1

EN 14363, "Railway applications - Testing and Simulation for the Acceptance of Running Characteristics of Railway Vehicles - Running Behaviour and Stationary Tests", European Committee for Standardization (CEN), Brussels, 2005.

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