Mr Whippy
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| posted on 15/2/08 at 01:35 PM |
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mindless rambling zzzzzzzzzzzzzzzzzzzzzzzzz
This may be a dumb post but then most have odd today.
I was thinking about these hybrid cars and funnily enough trains! Why do diesel trains usually run a generator rather than direct drive to the wheels?
I’m assuming it is to do with not needing propshafts, gearboxes etc but could this be applied to a car, ditch the gearbox and replace with a
generator. That way the engine can run at its optimum speed at all times rather than plowing through the gears. Don’t know just thinking aloud. There
would obviously be losses between the generator and motors but gears do that anyway plus a small battery pack could spin up the generator to start the
engine thus allowing the engine to be turned of in heavy traffic.
Fridays…don’t you just hate them, stupidly I finished all my work this morning and am now just booooorrrreeeedddd 
Fame is when your old car is plastered all over the internet
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tegwin
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| posted on 15/2/08 at 01:39 PM |
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I was always lead to believe it had something to do with torque...
If you have a large train and a small diesel engine, you would have to spank its nuts off to get the train moving...
Whereas if you use that small engine to generate electricity, and or hydraulic pressure to drive the train you get lots of torque, imediately.
Also makes geting the power to sepperate bogeys a bit easier!
I know the feeling about being bored....I have a week of it before the students get back from half term...
[Edited on 15/2/08 by tegwin]
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Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
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iank
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| posted on 15/2/08 at 01:45 PM |
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Well done that man, you've just invented the Toyota Prius 
Or more accurately as you're talking diesel the new Peugeot 308 due at the end of this year.
http://www.autoexpress.co.uk/news/autoexpressnews/207600/peugeot_308.html
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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RazMan
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| posted on 15/2/08 at 01:46 PM |
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It makes sense when you consider that electric motors often produce their maximum torque at minimum revs.
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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Mr Whippy
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| posted on 15/2/08 at 01:46 PM |
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You’re probably right, I have cutaway of a diesel electric and it has a small substation inside and lots of switch gear.
Fame is when your old car is plastered all over the internet
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Mr Whippy
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| posted on 15/2/08 at 01:49 PM |
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quote:
Originally posted by iank
Well done that man, you've just invented the Toyota Prius
Or more accurately as you're talking diesel the new Peugeot 308 due at the end of this year.
http://www.autoexpress.co.uk/news/autoexpressnews/207600/peugeot_308.html
not really as that still has a gearbox, why bother with one?
Fame is when your old car is plastered all over the internet
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02GF74
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| posted on 15/2/08 at 01:50 PM |
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quote:
Originally posted by RazMan
It makes sense when you consider that electric motors often produce their maximum torque at minimum revs.
100% correct. Don't ask me how I found that out..
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dmottaway
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| posted on 15/2/08 at 02:04 PM |
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a new advertisement on the television (over here) praising the economies of rail transport claims that the trains can move 1 ton of cargo 424 miles on
1 gallon of fuel!
does this mean that our cars should get 848 mpg, given they wight about 1000 pounds?
dave
Somewhere, in Texas, a village is missing its idiot.
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Macbeast
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| posted on 15/2/08 at 02:14 PM |
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So you replace an engine and gearbox with an engine, generator and electric motor.
Doesn't do much for your power to weight ratio.
Put a bike engine in it 
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ditchlewis
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| posted on 15/2/08 at 02:20 PM |
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mr Whippys right,
all the current hybrids have engines that drive the wheels. what is proposed i think is that the generator has no gearbox or connection to the wheels,
just a cable running to the electric motors.
if you used 4 motors one for each wheel, you would have would have 4 wheel drive with little weight or complexity.
the generator could run at max efficency at all times.
i remamber say 15 years ago volvo looking at a diesel turbine generator driving electric motors in a car , the concept car was white and aero dynamic,
but nothing came of it. turbines are very reliable efficent..with a jet sound track
i cant see why it would not work. what are the common out puts of small generators?
ditch
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Mr Whippy
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| posted on 15/2/08 at 02:23 PM |
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yip that's what I was on about
Fame is when your old car is plastered all over the internet
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ditchlewis
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| posted on 15/2/08 at 02:28 PM |
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remember all the posts about the Jet powered 7 and jet cars in general, and how bad the throttle lag would be well in this application there
would be zero lag as they would be running at a constant speed and the electric motors give instant responce
ditch
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onzarob
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| posted on 15/2/08 at 02:50 PM |
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quote:
Originally posted by ditchlewis
mwith a jet sound track
ditch
Noise is a very big issue, as you all know when a Intercity goes past
Electric motors are more efficient well 75% or more in real life. a petrol engine is 33% efficient (best case)
So it makes sense to use electric motors. problem is powering them.
Sun...too intermittent,expensive
Batteries Too heavy,expensive
Diesel/turbine engine turning a generator turning a motor...too heavy/complex/noisy
See the size of a diesel engine and the number of people in it one or two. don't count the train part
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dhutch
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| posted on 15/2/08 at 03:33 PM |
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Yeah, as i understand it its just convenence really.
- Otherwise, to move such a heavy item, with such a small engine, you would need about 30gear changes. Like a big truck.
- However ofcause you get losses, all the generators/motors/switchgear get hot. Which is all loss.
The real question is why dont we have deisal-electric lorrys if we have deisal electric trains. Or to flip it on its head, why not have the train
driver go though a rook of gears like lorry drivers do.
My only though on the matter is that wieght for weight, the rolling resistance of a train is far lower than that of a lorry. So on a lorry the losses
are very much more signifcant.
- On an average journey i think trains use something daft like 75% of there power in the first two miles from each stop. The rest of the time there
really just coasting...
Ofcause there are always exceptions. And there are deisal mechanical trains around.
And as a side topic inter connecting with the prius comments. Does anyone know anthing about the 'hybid' (deisal electric with batterys)
hst set running up and down loughboroughs GCR?
- Ive seen it many times, stuck my nose in it while ive been down the locoshed. But never known anything about its mechanics. Presumably it has a
smaller, or slower running engine, normalish motors, and then the batterys to smooth out the shortfall, and maybe partake in some regenerative
breaking? Anyway, its yellow and an a hst, so i cant be too bad.
BET anyone?
Daniel
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Simon
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| posted on 15/2/08 at 09:42 PM |
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Turbine powered cars would work fine if people got around the idea of one big one (which like a big turbo spooling up) and replacing it with several
smaller units.
Turbines are much more efficient at high altitude, which puts us out of the equation.
A generator and electric motors are all very well, until you realise the generator has an internal combustion power source.
That Peugeot only manages 6mpg more than the official figs for the Rover 25 TD
Enf of life needs to start being taken into consideration for emmissions and disposal of battery parts etc.
ATB
Simon
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