Mechatronic bogie heralds 250 km/h on Swedish tracks

Riding the Gröna Tåget test train with mechatronic bogies, Murray Hughes reports on the Swedish research programme to develop the next generation of high speed train that will replace the X2000

SPEED RECORDS make headlines, none more so than the carefully staged event in France on April 3 this year. Rather less publicity surrounded a national speed record attained in Sweden on July 18 which marked a significant stage in a research project from which all the Nordic railways stand to benefit.

On that day a specially-equipped Regina trainset was timed at 282 km/h on the Skövde — Töreboda section of the Stockholm — Göteborg main line. The prime objective was not to set a record, but to check the performance of an innovative bogie design that forms a key element in plans to develop a new generation of Swedish high speed trains.

The test train was two-car Regina set 062, which is the main focus of two major research programmes — the Gröna Tåget (Green Train) concept and Bombardier's Regina 250 project.

Gröna Tåget was initiated by Banverket and is supported by 12 other organisations (Table I). Its aim is to develop the specification for a 250 km/h train to replace the X2000 tilting train fleet that operates Sweden's fastest inter-city services. The new trains will be needed in the next five to 10 years, and Bombardier's Regina 250 project is closely linked to the same objective.

Nine research areas are addressed in the Gröna Tåget programme with 15 specific projects and five to 10 smaller projects running in parallel. Among the most significant is the development of a bogie with active lateral suspension. Two such bogies have been fitted under one car of the test train, which, following approval by safety authority Järnvägsstyrelsen, is expected to begin carrying passengers in revenue service this autumn.

During a Gröna Tåget presentation in Stockholm on August 8, Prof Evert Andersson of the Royal Institute of Technology, who is Programme Co-ordinator, Technology, explained why a high speed train cannot be ordered off the shelf from suppliers elsewhere in Europe. As one of 'six to eight countries able to develop trains for 200 km/h or more', Sweden wants to exert some of its own influence on train design and standardisation.

More significant, perhaps, is that TSIs and Euronorms ignore some important requirements for operation in Sweden and other Nordic countries. Andersson cited the use of mixed traffic lines, the problem of track defects arising from frost upheaval, the use of short trains to serve a modest population and the related need to have two pantographs raised in close proximity when trains are running in multiple.

Radial steering

Sweden's network includes many lines with sharp curves, and this explains why much of the Gröna Tåget research effort is geared to developing track-friendly bogies. The first large-scale application of radial self-steering bogies in Sweden was in the 1980s after Swedish State Railways found that excessive flange wear was occurring on its main lines. Orders were placed for radial-steering bogies to equip 375 loco-hauled coaches. The move was successful enough for subsequent EMU orders to specify radial steering bogies, and 458 EMU cars now in use in the Nordic countries are so equipped. They include the Øresund EMUs which operate at up to 180 km/h and the Flytoget sets in Norway which reach 210 km/h.

Investigations as part of the Gröna Tåget programme looked at how stiff the guidance of the wheelset should be. Bogies with guidance that is too soft, without adequate damping, tend to exhibit instability or hunting, even at speeds below 100 km/h, so the research focused on resolving the conflict between curving ability and dynamic stability.

Radial self-steering bogies with 'soft' and 'medium' guiding stiffness were tested in summer 2006 and again in 2007 using simulations and field tests with instrumented force-measuring wheels developed by Interfleet Technology. Stability criteria on straight track were met for both settings at speeds of well over 250 km/h with lateral track forces remaining within 50 to 65% of UIC limit values. The test run on July 26 2006 set a Swedish speed record of 281 km/h that was exceeded just under a year later by 1 km/h.

The next step was to test a new bogie with electronically-controlled active lateral suspension. Termed the mechatronic bogie, this features accelerometers on the axleboxes that measure lateral acceleration caused by track imperfections. Signals are sent to a bogie-mounted processor, which outputs commands to an electro-mechanical actuator that steers the axle in the opposite direction. Each axle is independently controlled, and the entire process is achieved in real time.

A bogie with this feature was tested on the roller-rig at DB's research institute in München in 2003, when a speed of 400 km/h was simulated. The series of tests happened to be the last on the roller-rig before it was closed, and engineers were able to introduce a series of malfunctions at high speed to see what would happen. The ultimate test came when power to the control equipment was cut off while the wheels were rotating at a speed equivalent to 350 km/h. No derailment occurred, confirming the basic principles of the design.

Trials were next conducted in 2004 with a mechatronic bogie mounted under one of Deutsche Bahn's Class 612 tilting trainsets on loops of 300 m and 700 m radius at the Siemens Wegberg-Wildenrath test facility.

Two mechatronic bogies with active lateral suspension were then prepared for testing as part of the Gröna Tåget and Regina 250 programmes in summer 2007. The goal was to reduce lateral vibration to achieve the same ride comfort at 250 km/h as on a train without active suspension at 200 km/h.

It was during these trials that the test train set the new record. The results of the trials were sufficiently encouraging for the research teams to stage a demonstration run on August 8 between Stockholm and Västerås when a speed of 251 km/h was achieved on the outward and return trips between Enköping and Västerås. Ride quality in the car fitted with mechatronic bogies was noticeably superior to that in the adjacent vehicle with bogies featuring passive radial steering, and the difference was especially evident for standing passengers.

Benefits

Mechatronic bogies offer several benefits which Bombardier listed on August 8 as reduced wheel wear, higher curving speeds and less energy consumption. UIC certification tests were to be carried out at 200 km/h, and the bogie had been developed to 'series state'. According to Guenther Himmelstein of Bombardier, who with Richard Schneider, Vice-President, Product Engineering Integrity, is one of the 'fathers' of the mechatronic bogie, a series version would in practice require 'review of the whole design' as, for example, the electronics pack is currently mounted on top of the bogie whereas it could be fitted inside a transom.

The design dispenses with yaw dampers between the body and bogie, obviating the need for large brackets and achieving a useful weight saving. A related feature is the requirement to use a hold-off device to keep the car body centred when passing through curves. This has spin-off benefits as it permits the use of a wider body and improves stability in high cross-winds.

Wide bodies — already exploited in the Regina design — are one of several key design features of Sweden's future high speed train. Thanks largely to BV's generous loading gauge, body width can be increased to 3?270 mm, which allows comfortable 3+2 seating. A 27 m long car would seat 90 passengers compared with 74 in a body only 2?670 mm wide, and a possible Gröna Tåget formation of four wide-bodied cars able to seat 310 passengers would be just 107 m long. This compares with 165 m for an X2000 set with the same capacity.

Faster journeys

Oskar Fröidh of the Royal Institute of Technology said on August 8 that the future high speed train would knock 15 min off the non-stop Stockholm – Göteborg timing achieved by today's X2000 trainsets, currently 2 h 46 min, at the same time cutting energy consumption by 20% to 30%. The faster timing for the 455 km trip assumes that some improvements are made to the infrastructure, including resignalling, work on the catenary and possibly the elimination of level crossings.

In the longer term, construction of the 150 km Ostlänken (Eastern Link) forming the first part of the Götaland Line project would provide the opportunity for dramatic time savings, with the Stockholm — Malmö timing of 4 h 10 min reduced to 3 h 20 min using Gröna Tåget rolling stock. The 150 km double track link would run between Järna and Linköping, and current plans envisage that a start on construction could be made by 2015, according to Anders Senestad, City Commissioner in Söderköping.

The 190 km Botniabanan between Nyland and Umeå along the northern part of Sweden's east coast is meanwhile due to open in 2010-11, and estimated timing for a Gröna Tåget set over the 737 km from Stockholm to Umeå is 5 h 5 min.

Next steps

Further trials with the mechatronic bogie are envisaged. Speed has until now been limited by the traction power supply, even though the line voltage was increased from 15 kV to 18 kV for the record runs. Next summer another opportunity will present itself, and Richard Schneider thinks 'everyone will take the chance to achieve 300 km/h'.

Other research as part of the Gröna Tåget programme between now and 2010 will cover tilting systems and measures to reduce motion sickness, market demand, performance requirements, train configurations, cost and revenue analysis, and interior design.

Work has already been carried out on current collection at high speed, and the Gröna Tåget test train sports a WBL88 Schunk pantograph specially developed for Swedish conditions.

A major development in prospect is the use of permanent magnet traction motors, which Bombardier plans to test in 2008. Apart from the advantage of lower weight and less volume, this opens up the possibility of attaching the motor directly to the wheel. Permanent magnet motors would also be able to brake the train down to 0 km/h, according to Schneider, obviating the need for a mechanical brake other than for parking.

According to Tohmmy Bustad, Banverket's Programme Manager for Gröna Tåget, Banverket is contributing SKr50m towards the programme in 2006-10, and the other partners will supply work and services worth about SKr100m to SKr150m; largest contributor is Bombarder with its Regina 250 project.

Table I. Organisations participating in Sweden's Gröna Tåget project

Swedish National Rail Administration (Banverket)
SJ AB
Bombardier Sweden AB
AB Transitio
Royal Institute of Technology (KTH)
Chalmers University of Technology
Swedish National Road & Transport Research Institute (VTI)
Interfleet Technology AB
Swedish Government Agency for Innovative Systems (Vinnova)
Transrail Sweden AB
Svenska Tågkompaniet AB
Konstfack (University College of Arts, Crafts & Design)
Branschföreningen Tå goperatörna

CAPTION: Guenther Himmelstein, Project Manager - Mechatronic Bogies for Regina 250 at Bombardier, stands in front of the two-car test train that was demonstrated between Stockholm and Västerås on August 8, reaching a speed of 251 km/h
CAPTION: The mechatronic bogie has actuators consisting of vertically-mounted leaf springs designed to achieve high stiffness in the longitudinal direction as the forces are transmitted to the axlebox
CAPTION: This bogie with passive radial steering mounted under one car of the Regina test train is used to compare ride quality with the mechatronic bogies?
CAPTION: On board the test train on August 8 2007 when a speed of 251 km/h was reached between Stockholm and Västerås