How do Spanish trains stay on the rails?

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abenn
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How do Spanish trains stay on the rails?

Postby abenn » Mon Jan 28, 2019 10:44 am

Watching a TV programme recently -- Chris Tarrant I think -- there was a bit showing how Spain's high-speed trains have independent wheels, rather than pairs of wheels on a solid axle. I've always understood that the solid axle keeping the wheels turning as one, combined with the slight bevel on the tyres, was the reason the wheel sets didn't hunt from side to side when running. That principle is neatly demonstrated at York railway museum.

So, how do the Spanish achieve a smooth ride without hunting? In the film there appeared to be no mechanical connection between opposite wheels in the bogie, and they were also shown being moved in an out to change their gauge.

Bigmet
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Re: How do Spanish trains stay on the rails?

Postby Bigmet » Mon Jan 28, 2019 11:24 am

There's a ton of technical information available on line provided you know the magic word 'Talgo' which is the manufacturer of this system.

First thing to remember about your specific question is that while a rigid axle between the two wheels is the simplest method for delivering the self centering effect of a pair of coned tyres, (aided by running on rails with a slight inward cant) it isn't the only way. Provided that the structure in which the independent wheels are mounted maintains them in the constant relationship that an axle naturally provides, the self centering effect generated by the pair of coned wheels still occurs.

There 's a lot more to the Talgo system than this. At the price of a more complex construction it allows higher speeds on a rail infrastructure that has much small radius curvature, and has been developed to permit rolling gauge transitions that you have seen.

abenn
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Re: How do Spanish trains stay on the rails?

Postby abenn » Mon Jan 28, 2019 11:32 am

Thanks Bigmet. I'll check out what the internet has to say about 'Talgo'.

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Bufferstop
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Re: How do Spanish trains stay on the rails?

Postby Bufferstop » Mon Jan 28, 2019 7:51 pm

Talgo's first coaches were like sections of aircraft fuselage mounted on boat trailers each one connected to the centre point of the pair of wheels on the one in front. The latest designs have replaced the rear beam assembly with a portal frame that suspends the coach body at the top above the wheels allowing it swing naturally as the train leans into bends, giving similar effect as the APT and the Pendolino with far less complication. God job, the gauge changing wheels are complication enough. The train that was involved in the catastrophic derailment a couple of years ago was a Talgo set with an electric loco on each end with a cabless diesel loco inserted between each loco and the set.no wonder the driver allowed it to run away with him.
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Bigmet
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Re: How do Spanish trains stay on the rails?

Postby Bigmet » Tue Jan 29, 2019 9:45 am

Bufferstop wrote:...The train that was involved in the catastrophic derailment a couple of years ago was a Talgo set with an electric loco on each end with a cabless diesel loco inserted between each loco and the set.no wonder the driver allowed it to run away with him.

How time flies. I had to go and look them up: the major crash in Spain was July 2013, and the one on the western side of the USA in 2017.

The Spanish crash was attributed to a driver with a liking for speed and quite possibly inadequate route knowledge, and he was jailed. Whether anything came of the criticism of RENFE's operational practise that the train's route took it off the high speed signal controlled system section where the system puts the brakes on in event of overspeed, onto ordinary tracks where the signal system only warns the driver of overspeed hazard; that I don't know.

The crash in the States was the first run on a new route and the driver appears to have mistaken his position, thought he was still a mile from the new route's speed restriction when he was actually entering it. So, inadequate route knowledge as the cause.

The major lesson I read from all this is that it is imperative that Talgo trains don't come off the tracks, because when they do it is 'all fall apart' time. The construction is not as strong or stable as conventional rolling stock. (Personally I would say it's an inadequate design, as foreseeable hazards such as collision caused by derailment obstruction from another train on a parallel track will lead to casualties far worse than those with conventional stock. In the case of the USA, the Talgo system was permitted to go into service on 'grandfather rights' as it could not meet previously instituted safety standards. This seems very odd, 'grandfathering' something which is a novel introduction to a system...)

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Bufferstop
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Re: How do Spanish trains stay on the rails?

Postby Bufferstop » Tue Jan 29, 2019 7:41 pm

Those petrolheads from the Grand Tour managed to reinvent the original Talgo design for a stunt they did on the Great Central. They fitted rail wheels to a large Merc and a motley collection of caravans, put towing hitches on the back of everything and connected it up. It worked :o
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Bigmet
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Re: How do Spanish trains stay on the rails?

Postby Bigmet » Tue Jan 29, 2019 9:09 pm

Bufferstop wrote:... It worked :o

Well, sort of. The Sinclair C5 of the railway? Only slightly less funny than the Toybota, so pretty good as entertainment.

abenn
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Re: How do Spanish trains stay on the rails?

Postby abenn » Tue Jan 29, 2019 9:18 pm

Well, I've had a good look at the internet Talgo postings, and I get the general idea that the wheels are positioned by computer (and mechanical linkages presumably) to run at the optimum position on the rail. But they seem to be protecting their patents by not putting much detail on the internet :(

The simplified tilting is interesting, though, as you say, it can result in a more 'fragile' coach than traditional and Pendolino designs.


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