Keywords: high-speed, track-friendliness, running gear, bogies, active technology, stability, radial steering.

Since 2005 a comprehensive research and development programme, financed by the Swedish Rail Administration (Banverket), Gröna Tåget (Green Train), is being carried out in Sweden. In close coordination with Banverket's programme Bombardier is developing and testing new technologies. The aim of the joint effort is to support development of the next generation of high-speed trains for Nordic conditions. The overall focus is to increase vehicle speed from today's 200 to 250-300 km/h.

The running gear development is carried out in close cooperation between Bombardier and the Royal Institute of Technology (KTH) in Stockholm. On-track tests are performed with a two-car train set of an existing REGINA vehicle where the bogies are replaced with new ones. Three new technologies are tested:

• A passive self-steering "soft" bogie for operational speeds of 250 to 300 km/h with good steering capability in curves. Soft bogie means low longitudinal wheelset guidance stiffness in relation to the desired maximum speed.
• An active lateral suspension including also a hold-off-device function to improve ride comfort and to enable high cant deficiency in curves without bump stop contact. Further, a wider carbody is possible due to a smaller lateral suspension travel.
• The FLEXX Tronic technology (part of BOMBARDIER's ECO4^TM portfolio): a mechatronic bogie actively controlling the wheelset motions with actuators attached to the bogie frame. The mechatronic bogie provides an even better curving performance than a passive soft bogie, still ensuring running stability at high speeds.

In the paper the three new technologies will be described and test results presented. Focus will always be on the challenge of balancing the contradictory demands of good running behaviour at high speeds on straight track on the one hand and good curving performance with low track damage and maintained good ride comfort on the other hand.

The results presented show that almost all goals that were set up in the beginning of the project are achieved. The passive radial self-steering bogie with and without active suspension is today approved in Sweden for 250 km/h service speed with passengers. The active radial steering bogie is approved to be operated with passengers at 200 km/h. Both the passive and the active steering bogie have shown that it is possible to design running gear that permit high speeds on straight track while retaining a good curving performance resulting in low wheel and track damage. This minimises maintenance costs and will lead to low track access charges once such systems are introduced.

Active lateral suspension does significantly improve ride comfort, especially in large-radius curves where the acceleration levels are reduced both by the hold-off device (HOD) and the dynamic control. The HOD function also enables wider carbodies, higher speeds in curves and a reduced sensitivity to high cross-winds.

With the FLEXX Tronic technology Bombardier Transportation is developing a modular platform that allows combinations of all technologies described in this article, i.e. both passive and active steering is possible to combine with the active lateral suspension technology.

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