Bogie / Chassis connections

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4 Jul 2011
Hi all... for a while I've been pondering a couple of things about how bogies connect with the chassis of a rail vehicle.
I know this will be simple stuff to somebody out there, perhaps you could enlighten me!

1) I assume bogies have some sort of central pivot pin, or bearing, which the vehicle chassis sits on. Does this just rely on gravity (I assume not) or is there a more positive connection? I've seen rail accident photos where vehicles seem to fairly readily part company with their bogies!
2) Some vehicles have airbags, springs, dampers etc between the rotating bogie and the body of the vehicle. For example, airbags on Class 150 DMUs, springs on Class 87 (photos attached). How do these accommodate the rotation of the bogies relative to the fixed body of the vehicle?
3) Thinking of DMUs with mechanical transmission - how does the engine/gearbox fixed to the vehicle chassis, transfer power to the bogies, which can rotate relative to the chassis?

Appreciate any explanations!


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RailUK Forums


3 Jul 2009
I can give an example of a Desiro and I expect other trains share a similar design.

The bolster is bolted directly to the bodyshell. The bolster also has a 'tunnel' to accommodate a cardan shaft (if DMU). At the lower end of the bolsters tunnel there is a tapered pin which the centre pivot assembly attaches to.

The centre pivot assembly (basically a large bonded rubber bush) fits onto the tapered pin and is bolted to it (cup & cone). There are also two tie rods bolted between the centre pivot assembly and the bogie frame that transmits traction and brake forces. These can also cope with vertical lift as the train bounces about over points, airbags inflate/deflate etc.

That is what's essentially keeping the frame / bolster attached to the bodyshell.

Air bags are bolted at the top to the bolster, but at the bottom just sits in the frame, located by a spigot. The bags themselves are by design flexible enough to cope with the twist of the bogie.

The coil springs on that Class 87 look to be located by spigots on the underframe at one end and the bogie frame at the other. I've not been under one of those but I expect there will be a similar arrangement to what I've described above where by there will some sort of anchor arrangement between underframe & bogie frame but with a degree of flex but it will be the springs that are actually doing the work of supporting the bodyshell. As per the airbags, these will be very flexible to accommodate bogie rotation.

DMU driveline (should be fairly universal this)...

The driveline uses cardan shafts. Just like on a bus or truck, these have universal joints and a sliding section and are flanged & bolted directly onto the engine flywheel, transmission and final drive input / output shafts. There is plenty of room for manoeuvre.

Some books to keep an eye out for.

Diesel Traction - Manual for Enginemen
BR Equipment Vol 1
BR Equipment Vol 2
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16 Oct 2019
Thanks 37057, that's very useful.

I've stumbled across a webpage which explains a lot of what I was pondering, thought I'd share in case it's useful to others.
I can't remember which series it was on TV last year, whether a Great Western one or the Transpennine one, I THINK the Transpennine one - there was some footage showing engineers swapping a bogie which explained and showed how they were mounted on that particular class.

I'm sure its available on demand (can't remember the channel), if not the episodes are probably on YouTube by now.
An interesting watch!
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