DMUs

[asylumxl]

Personally I don't think DMU's should be on such long distance trains, the uncomfortablel seats and engine vibration is annoying.

They're DEMUs.

 

[Zoe]

They're DEMUs.

Why are DEMUs not considered to be a type of DMU? DMU stands for Diesel Multiple Unit and this makes no reference to the transmission. DHMU/DMMU/DHMMU are rarely used and it seems acceptable to call all of these Diesel Multiple Units but for some reason you can't call a DEMU a type of Diesel Multiple Unit.

 

[asylumxl]

Why are DEMUs not considered to be a type of DMU? DMU stands for Diesel Multiple Unit and this makes no reference to the transmission. DHMU/DMMU/DHMMU are rarely used and it seems acceptable to call all of these Diesel Multiple Units but for some reason you can't call a DEMU a type of Diesel Multiple Unit.

As far as I can see the majority of people/companies use the term DMU to mean a diesel mechanical multiple unit rather than a DEMU. This can be seen on this very forum, in company brochures and many other places.

If we are going to be so very pedantic, perhaps everyone should attempt to be more accurate and concise, I mean afterall, I could call you a "thing", which while technically accurate, isn't very concise is it?

 

[yorkie]

A DMU is a DMU, no matter how you doll it up.

I agree, if it's a multiple unit, and it runs on diesel, it's a DMU. However most diesel multiple units have traditionally tended to have mechanical transmission (DMMU), so when people hear of 'DMU' they tend to assume mechanical transmission, though hydraulic transmission seems to be making a comeback (e.g. Class 185). Very rarely are the abbreviations 'DMMU' or 'DHMU' used.

Diesel electric is, arguably, superior, and in some cases may be able to work in multiple with an EMU (e.g. ex-Southern region units) and have electric traction motors, just like EMUs, so people tend to use the abbreviation DEMU to differentiate them.

Most passengers, they won't notice, or be interested, in the differences.

 

[Bill EWS]

Note: split from What is wrong with CrossCountry?

...Personally I don't think DMU's should be on such long distance trains, the uncomfortablel seats and engine vibration is annoying...

..A DMU is a DMU, no matter how you doll it up....

 

[Cherry_Picker]

I agree, if it's a multiple unit, and it runs on diesel, it's a DMU. However most diesel multiple units have traditionally tended to have mechanical transmission (DMMU), so when people hear of 'DMU' they tend to assume mechanical transmission, though hydraulic transmission seems to be making a comeback (e.g. Class 185). Very rarely are the abbreviations 'DMMU' or 'DHMU' used.

Really? I'd always naturally assumed the opposite and that most DMUs had hydraulic transmission. Maybe it is an age thing or a where you live thing, I started becoming aware of such things in the 1990s in the midlands so what I think of when I think of a DMU are things like sprinters and turbostars. 158s, 165s, 168s, 170s and the like, all of which have a hydraulic transmission. It's only really the 172s that I've seen with a mechanical transmission.

I don't really know that much about how diesel electric works but I am of the understanding that the main advantage is because an electric motor is the thing making the wheels move then acceleration can be faster due to the fact that you don't have to wait for things to be spinning around at top speed in high gears before you can use all the available power. I'm pretty sure my understanding is wrong though so I'd be more than happy for somebody who knows a bit more about them to expand on the point.

 

[61653 HTAFC]

As far as I can see the majority of people/companies use the term DMU to mean a diesel mechanical multiple unit rather than a DEMU. This can be seen on this very forum, in company brochures and many other places.

If we are going to be so very pedantic, perhaps everyone should attempt to be more accurate and concise, I mean afterall, I could call you a "thing", which while technically accurate, isn't very concise is it?

They're DEMUs.

Pot/Kettle:roll:

Just saying...

 

[edwin_m]

Electric transmission is usually used when more power is needed, hence practically universal on locomotives. It also tends to be used on higher-speed units, not only because these are usually higher-powered but also because a mechanical or hydraulic transmission needs more "gears" or equivalent so gets more complicated in a wider speed range.

The link below is a fairly simple explanation of mechanical transmission as fitted to first-generation DMUs.

http://www.railcar.co.uk/technology/introduction.html

Even the transmissions that are described as mechanical contain a fluid flywheel which is a hydraulic component. The difference is that the "mechanical" transmissions have a multi-speed gearbox, with the fluid flywheel acting like a clutch. The hydraulic transmissions have a torque convertor doing the job of the gearbox.

All the second and third generation units numbered from class 140 upwards use a hydraulic transmission with the exception of 150002 as built, the two class 151 and the class 172 which had/have something similar to the old mechanical arrangement.

 

[yorkie]

Really? I'd always naturally assumed the opposite and that most DMUs had hydraulic transmission.

Well, I did say traditionally!

And, when it comes to mechanical vs hydraulic, I am sorry but I am in the category of most regular passengers, who are not particularly interested (sorry!) and I find them to be boring - though I do quite like the old first generation DMUs, but not for their engines! I think some of the newer designs are not necessarily easy to categorise though, which is perhaps another reason why people don't tend to differentiate.

Now some of the diesel electrics, they are interesting!

And I totally agree it will vary depending on where you're based and used to.

 

[asylumxl]

Pot/Kettle:roll:

Just saying...

Welcome to the internet!

 

[RobShipway]

I think the Voyagers should be in a category of their own, as they are not true DEMU's such as the old Southern 205 & 207 DEMU trains, as the Voyagers cannot pick up power from the third rail tracks when they are working in the Southern Region and cannot use the OHL when running further north.

 

[bronzeonion]

I think the Voyagers should be in a category of their own, as they are not true DEMU's such as the old Southern 205 & 207 DEMU trains, as the Voyagers cannot pick up power from the third rail tracks when they are working in the Southern Region and cannot use the OHL when running further north.

I made this mistake till I learnt too, I thought 205s and 207s could pick up juice hence the category DEMU. They dont actually have the ability to pick up power from the 3rd rail.

 

[D365]

I think the Voyagers should be in a category of their own, as they are not true DEMU's such as the old Southern 205 & 207 DEMU trains, as the Voyagers cannot pick up power from the third rail tracks when they are working in the Southern Region and cannot use the OHL when running further north.

I made this mistake till I learnt too, I thought 205s and 207s could pick up juice hence the category DEMU. They dont actually have the ability to pick up power from the 3rd rail.

Yes, and then what would be about Class 210 (as-built)? HST 253-5 as well? IIRC when a MU can run off external electric and internal diesel traction it is know as an EDMU - see IEP.

 

[Peter Mugridge]

Yes, and then what would be about Class 210 (as-built)? HST 253-5 as well? IIRC when a MU can run off external electric and internal diesel traction it is know as an EDMU - see IEP.

The 210s never had external power collection though, either 3rd rail or overheads did they?

 

[D365]

The 210s never had external power collection though, either 3rd rail or overheads did they?

Yes, that's what I meant, once again I haven't made myself clear

 

[455driver]

A DMMU uses the engine, via a cardan shaft, to drive a gearbox which, via another cardan shaft, drives the final drive which moves the train.
A DEMU uses the engine to drive a generator (or alternator) which produces electricity to power a traction motor which, through a set of gears, moves the train.

 

[Mugby]

Forgive my ignorance but having read the book 'Second Generation Diesel Units' by Colin J Marsden, he describes Voyagers as Diesel Electric. This confuses me.

It's my understanding that the crankshaft of a Voyager engine goes into a gearbox from which a cardan shaft takes the drive to the powered axles via a differential.

So how can that arrangement be described as diesel electric?

 

[ainsworth74]

It's my understanding that the crankshaft of a Voyager engine goes into a gearbox from which a cardan shaft takes the drive to the powered axles via a differential.

As far as I'm aware the power is taken from the engine to a generator which is then used to power electric motors which drive the axles. Hence diesel electric.

 

[Mugby]

As far as I'm aware the power is taken from the engine to a generator which is then used to power electric motors which drive the axles. Hence diesel electric.

That's how I would describe an HST, or any of the old Southern Region DEMU's.

But on a Voyager, I'm certain I've seen a prop shaft (or cardan shaft) rotating beneath the bodywork.

 

[ainsworth74]

But on a Voyager, I'm certain I've seen a prop shaft (or cardan shaft) rotating beneath the bodywork.

I'm sure you have but it'll be between the engine and the generators or quite probably the motor and the axles.

 

[edwin_m]

In many high speed units the motor is in the body (under the floor) with a cardan shaft drive to the bogie, to reduce forces on the track. Penolinos do this and I'm pretty sure Voyagers do too.

 

[D6975]

Class 91s have the motors in the body too, cardan shafts down to the final drive on the bogies.

 

[tbtc]

...Personally I don't think DMU's should be on such long distance trains, the uncomfortablel seats and engine vibration is annoying...

I hate to go off topic and answer the point in the first post, but I'm really not sure what "uncomfortable seats" have to do with "DMUs".

Funnily enough you can have exactly the same seats in a DMU as you have in loco hauled carriages (and in an EMU too). Not all DMUs are Voyagers...

Engine vibration is something that gets mentioned a lot too, but I don't know how many normal passengers really notice this.

 

[455driver]

I'm sure you have but it'll be between the engine and the generators or quite probably the motor and the axles.

The shaft you can see runs between the traction motor and the final drive which is mounted on the axle.

 

[transmanche]

Engine vibration is something that gets mentioned a lot too, but I don't know how many normal passengers really notice this.

From some of the comments on here, you'd imagine it was like sitting on a washing machine doing a fast spin!

 

[tbtc]

From some of the comments on here, you'd imagine it was like sitting on a washing machine doing a fast spin!

True.

And, often the same people making this complaint are frothing about how good it is sitting in the front coach of an HST (though less good now the Valenta engines are quieter than their replacements).

I also like the "why bother electrifying- most passengers won't notice the difference between an EMU and a DMU" argument from the same people.

 

[455driver]

From some of the comments on here, you'd imagine it was like sitting on a washing machine doing a fast spin!

Dont knock it until you have tried it.

my other half tells me its quite "interesting".

 

[asylumxl]

Dont knock it until you have tried it.

my other half tells me its quite "interesting".

Probably the most fun she gets between you and her trips on a Voyager .

 

[455driver]

Probably the most fun she gets between you and her trips on a Voyager .

Oye we will have less.

Unlike my other half!

Maybe thats why she goes a bit cross eyed when we go to Yorkshire on the train?

 

[asylumxl]

Oye we will have less.

Unlike my other half!

Maybe thats why she goes a bit cross eyed when we go to Yorkshire on the train?

This thread just got a bit freaky...