Talk:Diesel multiple unit
|WikiProject Trains||(Rated Start-class, Mid-importance)|
DEMU should be merged with this article - not all DMU's are electric.
Very Eurocentric and Misleading 
After saying that railcars and in particular the American Rail Diesel Car are a type of DMU, it the goes on to claim that "In the USA, Federal Railway Administration rules effectively prohibit the type of lightweight DMUs used elsewhere in the world." I suspect this isn't true; at any rate, the discussion seems to be trying to claim this as a general name for the class of vehicles, when I'm tempted from the text to believe that it is the local usage of one system.
I'm finding increasingly that the terminological problem is going to need a more systematic solution. In any case something needs to be done/checked here. Mangoe 17:04, 22 July 2006 (UTC)
- First, The FRA quote is correct. The term DMU in North America is understood to mean self-propelled diesel cars that meet FRA crash requirements (think RDCs). Outside the US this encompasses all self-powered diesel cars, including light rail. In the US those are simply refered to as light rail. The FRA has stringent guidelines on crash-worthiness that prevents light rail and standard rail ("FRA crash compliant" is the technical term) from mixing. There is currently a TRB study being done to see how non-crash compliant vehicles can share with crash compliant at 
- Secondly, it is confusing for the article to then discuss MU Control under the North America section. This is a system where all the engines in a consist can be controlled from one single engine's control stand. Multiple-unit train touches on this, but only in the sense of electric streetcars.
- As you can see, these issues are getting muddied by the clashing terminology and safety requirements of US vs. Europe (Same reason the Acelas started service late). There is some discussion of solutions on Talk:Multiple_unit, and as time allows I will bring this to the attention of the trains wikiproject.
- Skabat169 16:01, 8 August 2006 (UTC)
- Well, the FRA doesn't prohibit "light" DMUs; the FRA does not allow them to share the rails with freight traffic. I recall coming across some American system which uses "time separation", a pompous way of saying that the passenger trains use the rails by day and the freight trains use it at night. Mangoe 16:22, 8 August 2006 (UTC)
Let's solve this now: Amtrak is encouraging the state of VT to use DMUs on its Vermonter line, in order to save money over the current GE Genesis-pulled trainsets. I see no mention of a "pompous" "time separation" agreement in any of the news articles, though one may surface over time. Mjl0509 13:55, 11 August 2006 (UTC)
- That's because the Colorado Rail Car units under discussion are FRA-compliant.
- There are too many articles in the whole "MU/railcar" complex, resulting in the issues about FRA compliance and light rail to be spread all over the place. Mangoe 15:38, 11 August 2006 (UTC)
It seems to me that this discussion really isn't about the accuracy of the statements made, but about their clarity, especially to those unfamiliar with the differences between North American and European regulations. I'm going to take a crack at improving THIS article, but I agree that there are probably already too many. That said, I am also going to suggest that someone write an article about the differences in American and European railroad regulations (along the lines of Comparison of Global Railroad Regulations). Simkid 19:26, 15 August 2006 (UTC)
- I like the comparison idea. I'm knowledgeable enough to write the North American viewpoint, is there someone out there knowledgeable enough to write the European side of it with me? Skabat169 14:24, 16 August 2006 (UTC)
- Well this is a first for Wikipedia... Eurocentric! Ha! Usually most articles bang on about America like it's the only place on the planet. Well it seems to have plenty about the USA in it now. I have to say I think the merge with DEMU wasn't done too well, they took the British DEMU history and shoved it wholesale into the DMU article, making it sound like those were all the DMUs we had. I've tried to correct this a bit and wrote a fair bit up, though the article is now starting to look rather "Britcentric". Afraid I can't help that, I don't know anything about foreign railways to be able to contribute meaningfully. --188.8.131.52 02:40, 16 June 2007 (UTC)
Ierland and Japan have now been added.--Freetown 03:43, 17 August 2007 (UTC)
It's not Euro centric any more.--Pine oak 03:09, 19 August 2007 (UTC)
Nope now it just bangs on about America, like the rest of the English language Wikipedia. 184.108.40.206 23:11, 20 August 2007 (UTC)
- I cleaned it up a fair bit the other day - I felt it had way too much British stuff in there before, at one point there was a history of a few classes that already had detailed articles on them. (I'm an Aussie by the way) Perhaps a cull of the various USA proposals might be worthwhile? To me each countries subsection should mention (as an example) 'we started with XYZ class on QWE services, then moved to ABC class and now use DEF' as a jumping off point to the individual classes, otherwise this article just gets tool long. If you want to go on about it in more details about your country, then make a sub page like List of British Rail diesel multiple unit classes or Multiple Units of Ireland. Wongm 05:27, 21 August 2007 (UTC)
I am attempting to seperate all the discussion of MU as in train control into the article Multiple-unit train control, leaving all discussion of MU the cars for this article, EMU, and Multiple unit. As such, I moved the discussion of MU Train Control to that article and removed a few links that seemed out of place without it. If people think this should be undone, I would prefer that it's discussed here or at Talk:Multiple-unit_train_control first. Thanks. Skabat169 05:11, 9 June 2007 (UTC)
Concerning the advantages of diesel-electric locomotive or DEMU power 
Direct-drive diesel locomotive would need an impractical number of gears to keep the engine within its powerband; coupling the diesel to a generator eliminates this problem. There seems to be a lack of explanation as to WHY. It should be emphasised that power still needs to be transmitted to the generator or alternator via a simple gearbox but this is advantageous because;
1) Mere cables transmit the power to the axle traction motors, not a complex system of rods
2) Sending power to a generator via a low powerband (i.e. diesel) is analogous to sending power to a propeller, in that one gear ratio is enough, unlike sending power to wheels, where several ratios are necessary. This is because the high friction between wheels and contact surface requires a low gear for takeoff to avoid stalling, and higher gears thereafter, since the output shaft moves relative to vehicle speed and would over-rev the engine if just one gear was available. In a generator or alternator, the force is magnetism, not a high friction surface so a high gear is fine since the magnetism is not great enough to stall the engine. The result is that the diesel-electric system puts the diesel’s low powerband to best use.
I really want an engineer to check the above!
- Yes but diesel locos that don't use an electrical transmission make use of this great thing called a torque converter, or a fluid coupling. That removes the needs for many gears, British Rail had a fleet of Diesel-Hydraulic locos. Indeed, I believe such transmissions were proved to be much more efficient in transmission of power than electrical systems. I remember hearing of a high-power experimental loco, however the reliability of the system employed was low.
--220.127.116.11 20:41, 11 August 2007 (UTC)
The original post here, which has now appeared in the article needs a complete rewrite! All the comparison stuff is based on DMU transmissions of the 50s and 60s, not the modern torque-converters fitted today, and as such is grossly inaccurate. —Preceding unsigned comment added by 18.104.22.168 (talk) 03:37, 10 November 2007 (UTC)
- "power still needs to be transmitted to the generator or alternator via a simple gearbox" This is incorrect. In most cases the diesel engine is direct-coupled to the generator. Biscuittin (talk) 15:26, 23 March 2009 (UTC)
- "diesel locos that don't use an electrical transmission make use of this great thing called a torque converter, or a fluid coupling. That removes the needs for many gears". This is only partially correct. A torque converter provides torque multiplication but this is not usually enough and there are likely to be between 2 and 4 gears as well. A fluid coupling is basically a clutch and does not provide any torque multiplication so 4, or more, gears will be needed. Biscuittin (talk) 15:41, 23 March 2009 (UTC)
Too many photos? 
I've noticed that the gallery sections has boatloads of photos in it now. If they aren't already in the articles on the individual trains than perhaps they should be moved there. Also, many of them have very detailed captions - I feel this page is for a world audience and drilling down to the exact operator, service run, number and livery is a bit too detailed. Possible just a 'very good image or two for each country, showing a distinctive or representative image of the most popular class of DMU, set in countryside that also represents the country. The millions of interior shots don't seem do much either - they pretty much just show 'our trains have seats'. Finally, there are a few photos of trains from countries that are not represented. If people who know about the DMUs in those countries please add a short history of DMUs in the country - when they were first introduced, links to classes, etc. Wongm 05:33, 21 August 2007 (UTC)
DMU vs, Diesel trains 
FRA "compliant" and European Railway compliant are basically the same "standard" ... both demand that a a passenger train meet the local railways crashworthiness standards. The fact that the Americans demand much more HEAVYWEIGHT passengers doesn't mean that europeans could accept LightRail units without them complying to heavy-rail standards ... that's why seemingly light rail trains (such as the bombardier Talent) are considered heavy rail. This "my DMU is better than yours" seems like the one about the french TGV's being or not EMU's ... the front/back cars don't carry passengers PRECISELY because of the crashworthiness demanded for traveling in european railwas above 100mph/ 160km/h (wich in recent years seems to be discarded as if it was not "stilish") Sotavento (talk) 04:56, 25 June 2009 (UTC)
- Yes, the problem is that people in the U.S. tend to call anything which doesn't meet their heavy-rail standards a light-rail vehicle, because it can only operate under light-rail rules in their country. So, when trains like the Talent and Desiro are accepted onto the main line in Europe, they take that to mean that European railway standards allow light-rail vehicles onto the main line without meeting 'real' (i.e. U.S.) heavy-rail requirements. David Arthur (talk) 21:17, 25 June 2009 (UTC)