The order for new trains for Thameslink 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

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!

Better brakes

The SF7000 bogies use three different forms of braking, but to save weight not all of them are fitted to each bogie. The power bogie has regenerative braking. This reverses the function of the motor, turning it into a generator and also acting as a brake as it consumes kinetic energy. It is the primary braking system as it saves money by reducing the power consumption of the train.

The power bogies are also fitted with tread brakes. Traditionally, these are inefficient, noisy brakes which work by rubbing a pad on the tyre of the flanged wheel. Crude freight wagons use these brakes – and have done for decades. Now, however, they use organic brake pads similar to those used on disc brakes, they are quiet and don’t damage the wheel, and they have the benefit of keeping the wheel clean and free from oil, leaf debris and other contaminants.

The trailing (unpowered) bogie has two large ventilated disc brakes mounted on each axle. These give good retardation and are used to balance the braking effect of the trailing and motor bogies. In any situation, the train control system uses a combination of all three methods of braking to give the most energy efficient performance.

The rest of the bogie has been designed around these weight-saving measures. To give good performance and low track wear there is a short wheelbase (only 2200mm on the motor bogie) and 820mm diameter wheels. Primary suspension is by rubber layer spring, with air springs for the secondary. The two electric motors on every motor bogie each deliver 235kW.

Lighter and leaner

Even small components have been examined, and trimmed where possible. The yaw damper brackets, which hang off the outside of the train and are thus peppered by ballast and other debris sucked off the train by the speed of its passing, were redesigned using hardened materials in thinner sections. To check that the resulting lighter bracket was strong enough, a sample was bombarded by stones shot from a catapult in the laboratory – and found to be stronger than the original.

The result of all this hard work is a massive weight saving over the current SF5000. The motor bogie is down from 9.3 tonnes to 6.3 (-32%) and the trailing bogie from 6.8 to 4.4 tonnes (-35%). And while the design is new, the technology is not – most of the major concepts in the new bogies have been used in earlier Siemens bogies, for example tread brakes were originally used on the SF2100 bogie for Shanghai.

So the first four bogies have been built – two motor bogies and two trailing bogies. They will now be subjected to a series of static tests at Graz, before being sent off to the train factory at Krefeld in Germany. There they will be fitted to the first two Desiro City body shells (which have also been built as part of the development programme without a signed Thameslink contract). By the middle of 2012 they will have started racking up thousands of kilometres of testing at Siemens’ own test track at Wildenrath.

Providing the contract is signed as anticipated, in March 2013 the first series production bogies will start to emerge from the Graz factory at a rate of up to 90 each month. The anticipated total of approx 2,400 bogies (1,200 each motor and trailer) represent less than 20% of the factory’s current capacity so, while a significant order, it will not cause manufacturing bottlenecks. After all, Graz is the Centre of Excellence.