Tucked away under most locomotives and railway carriages are a pair of bogies. Hidden from passengers below the platform edge, trains literally couldn’t run without them. How they perform markedly affects the ride and therefore the comfort of those passengers, yet they are often overlooked.

One of the world’s leading developers and manufacturers of bogies is Bombardier Transportation. The company has a large range of them for all applications, from heavy freight locomotives to trams. Bogies from the FLEXX family go under most of the electric and diesel multiple unit (EMU/DMU) trains that Bombardier produces, but they have to cope with a wide range of operational challenges depending on where the train is running and the job it is being asked to do.

While the bogies within the FLEXX family typically have different characteristics to suit a wide range of requirements, the common factor is that they have been developed by dedicated teams of highly-specialised engineers with a strong focus on the end goal – be it speed on dedicated or curved track, lighter weight, frame flexibility, low maintenance, or a combination of several of these factors. The result is a range of bogies for both high speed trains and high capacity metros, from China to Sweden, not to mention closer to home in the UK.

Comfort at speed

As an example, FLEXX Speed bogies are being delivered for the V300 Zefiro trains for Trenitalia which are manufactured in Italy by a partnership between Bombardier and Ansaldo Breda. These bogies were derived from a design that was originally developed for the Zefiro trains currently operating in China. However, as the Italian market has different requirements, certain modifications had to be made.

The design of the Italian routes placed additional demands on the suspension system. The requirement to run at 360 km/h (225mph) on track designed for 300 km/h (190mph) meant that special measures were needed to achieve a good ride comfort. So these latest bogies feature active lateral suspension which enables them to improve ride comfort while travelling at speed.

Containing operating costs is also important. With the first major overhaul scheduled only after five years, during which time the bogies may have run around 2.5 million km, the bogies had to be designed for minimal maintenance.

Mechatronic milestone

In a parallel development aimed particularly at routes with curved track, Bombardier has developed the FLEXX Tronic WAKO system. This is claimed to be the first fully-mechatronic suspension system in railway applications in that it combines mechanical and electrical engineering with computer technology. Its aim is to allow for higher speeds on curved tracks without compromising passenger comfort through DSC00413 [online]compensation of the natural roll movement of a train car body.

Integrated into the existing secondary suspension, FLEXX Tronic WAKO tilts the car body to the inside of the curve around a virtual rotating point generated by the anti-roll bar system. This enables trains, particularly double- deck coaches with a high centre of gravity, to run over 15% faster in curves. In turn, this brings shorter journey times on existing tracks, avoiding the need for significant infrastructure investment.

With a simple, fail-safe mechanical design and fully-redundant electronics and actuation, the new suspension also provides up to 100-times more reliability than achieved by classical active systems.

FLEXX Tronic WAKO will start its first service in 2015 with the FV-Dosto double-deck trains ordered by SBB in Switzerland. With 290 trains on order, and the provision for additional options, this fleet will form the backbone of SBB’s future railway service.

Flexible frame for challenging tracks

While high speed creates certain unique challenges, bogies at the other end of the product spectrum may have to deal with difficult track conditions such as those posed by intensively-used, high capacity metro systems.

Such is the case with the bogies that Bombardier has developed for London Underground’s Victoria line and the sub- surface line trains. These FLEXX Metro bogies feature an innovative flexible frame, which enables them to cope with the track irregularities inherent on this heavily used system.

Rubber-jointed flexible H-frames give improved performance on networks with challenging track twist. In addition, elastomeric components in the primary suspension give a high level of steering performance, helping to reduce noise and vibration.

As well as in London, specialist FLEXX Metro bogies have found applications as far afield as Bucharest and New Delhi.

Designed in the UK

The FLEXX Eco bogie was originally designed by and for the UK market and has subsequently became a global success. The product started life in the early 1990s as the ‘Advanced Suburban Bogie’ project, a joint development initiative between British Rail Research and private sector industry, with Eddie Searancke, now one of Bombardier’s leading bogie engineers, responsible for
its early development. He explains the progression of the project:

“We started with a list of objectives, including goals to reduce mass by 30% and aerodynamic drag by 40% compared with existing EMUbogies in the UK market. Bearing in mind that UK passenger bogies were already relatively lightweight in comparison with the rest of Europe, these were significant challenges, but encouraged us to literally ‘reinvent the wheel’.

“Consequently, we produced a radically different design of bogie which featured an inboard bearing design. This already gave us considerable advantages in terms of weight reduction. Coupled with a smaller wheelbase and hollow axles, it enabled us to achieve our target weight reduction and also made the bogie extremely aerodynamically efficient, hence also providing environmental benefits of improved energy efficiency.

“Another advantageous by-product of the inboard bearing design is its ease of maintenance and maintainability, with, for example, improved access to the wheels and brakes. The components were also designed with longevity and low maintainability in mind, principles which have endured to today’s FLEXX Eco bogie products.”

It is not just the improved access that contributes to better maintenance. The bogie also has a lower unspung mass, leading to lower wear on track, wheelsets and components. As a result, maintenance intervals have been extended significantly.

Following years of intensive testing on the UK network, as well as trials by Germany’s Deutsche Bahn and NSB (Norwegian Railways), the FLEXX Eco bogie was incorporated within the Class 220/222 Voyager and Meridian trains and Class 172 which form part of the Turbostar DMU family. There are now around 1,000 units in operation worldwide with the UK fleet alone operating over three million miles per week.

DSC00403 [online]The FLEXX Eco has also found applications in EMUs and it is no surprise that the bogie has been incorporated within Bombardier’s new generation Aventra train for the UK market.

In this application, the lightweight bogie design also helps with the reduction of the overall vehicle mass, meaning the new trains will be around 20% lighter than the current Electrostar.

Not just UK metro

A capability for high speed operation was not originally part of the FLEXX Eco concept. Nevertheless, it has been tested at 275km/h (170mph) on a Shinkansen in Japan and also at 392 km/h (245mph) beneath a German ICE2, demonstrating excellent stability. As a result, a development of this bogie has been chosen for Deutsche Bahn’s new ICx fleet, 300 of which have been ordered from Siemens. The first trains are due to enter service in 2016.

Reinforcing its versatility for all markets and applications, the FLEXX Eco platform will be used in the new C30 metro trains being provided by Bombardier for Stockholm’s Red Line with the first service planned for 2016. The bogie’s low weight and minimal impact on the track met key requirements for this contract.

All in all, that’s not a bad endorsement for a product originally designed by and for the UK. Today, Bombardier has approximately 35 dedicated bogie engineers within its 350-strong UK-based engineering team working on providing the latest in bogie technology to the world market.

Report by Jeanette Bowden