34 | the rail engineer | april 2012
feature
Bogies for
(Right) SF7000 trailer bogie showing the inside frame and inboard disc brakes.
order for new trains for T heThameslink has been controversial since it was first announced back on 16 June 2011. Siemens became the preferred bidder, and since then the national and local press has been awash with politicians, interest groups, trade unions and others urging the government to think again and hand the order to Siemens’ great rival, Bombardier. As well as pointing out the obvious, that Bombardier has a UK-based train assembly plant whereas Siemens doesn’t, one of the arguments put forward was that Bombardier has an established bogie for the new train, the German-built FLEXX Eco, whereas Siemens does not. So it was with great interest that the rail engineer set off for Graz in Austria for a first look at the SF7000 - the new Siemens bogie for Thameslink. But, hang on! The Thameslink contract STILL hasn’t been awarded (as of 12 March a DfT spokesman says the announcement is now expected “in the spring”!). So how have Siemens already built a new bogie for it? That was something else to ask about in Austria.
Styrian splendour
(from left) Three views of the SF7000 motor bogie: Tread brake and actuator; 235kW motor and gearbox and the bolster-less design is apparent.
Graz is two hours south of Vienna, and is south of the Alps so has a milder climate than much of the rest of Austria. The capital of Styria, Graz is Austria’s second city, although it has a population of only 250,000. The city encompasses six universities, whose 44,000 students add to the resident population. The Old Town is one of the best preserved medieval centres in Europe, and in 1999 it was added to the list of UNESCO world heritage sites. Bogies, and railway vehicles, have been built in Graz since the middle of the nineteenth century. J Weitzer Wagon Construction was founded in 1854, and by 1934 had combined with H D Schmid of Vienna to form Machinen and Waggonbau Schmid. The company went through several name
changes and owners until Siemens acquired 26% in 1992 and 100% by 2001. Production of vehicles ceased and today the Graz factory is Siemens’ centre of excellence for bogie production - for everything from trams to Velaro high speed trains.
Replacing the SF5000 The factory’s latest creation is the new SF7000. It is the bogie that will be used on the new Thameslink fleet, but as no firm order has been signed, why was it developed? Steve White, Siemens’ Service Director for the UK explained. “At the end of January 2007, it was decided that we needed a replacement for the Desiro UK trains that we had been supplying to the British market for the last few years. So a conceptual study was undertaken to define the specification for such a train. It would have to be lighter, and more energy efficient, than the trains which had gone before.” Siemens committed €50 million to develop the new train. When the Thameslink contract came along in 2009, it gave an added impetus to the programme as this was an obvious opportunity for the new design. The tender was submitted, but development continued as the new train, now named Desiro City, was going to be needed regardless of whether the company won the Thameslink contract or not. From a bogie point of view, the existing SF5000 bogie was still doing sterling service. Siemens trains, with SF5000 bogies, are the most reliable in service in the UK today. However, to get the maximum performance from
the new train, a new bogie would be needed. Helmut Ritter is Head of Engineering, Bogies, and to him fell the task of developing the new bogie. “We needed the new bogie to be lighter than the old SF5000 - much lighter,” he commented. “The reduced weight would consume less energy, and also be kinder to the track resulting in lower track access charges for our customers.”
Losing weight How to reduce the weight while keeping the same reliability? That was the question that Mr Ritter put to his design team. And the answer turned out to be a very different looking bogie indeed. For a start, the frame is inboard rather than outboard. This saves a considerable amount of weight in itself as far less steel plate is involved in its construction. However, having the frames between the wheels cuts down on the space for packaging the rest of the components, giving the designers more headaches. Next to go was the bolster. This normally rests on top of the bogie, and contains air reservoirs for the suspension and adds stiffness to the construction. It is also very heavy. The air reservoirs have been moved up into the car body, and the stiffness now results entirely from clever frame design. The steel axle is normally also very heavy. The new one isn’t - it’s hollow!