Diesel-electric cars...

Steel · 10-26-2006, 11:30 AM

And im not talking like the toyota/honda gasoline hybrids only with a diesel engine inside, i'm talking locomotive type diesel-electric cars. So. What do you guys think the feasibility of designing cars to be much the same as the locmotives are designed?

For those who don't know, diesel electric trains have a 2 stroke diesel motor in them (usually large, but that's understandable) that's conencted directly to an electric generator. The generator then powers electric motors that are attached directly to the wheels of the train. This seems to be a very efficient and compact design, considering there is no need for a 30 speed transmission, and the engine can run at peak efficiency (or idle) all the time.

I don't see why this couldnt work for cars. Obviously a car wouldnt need an engine displacing 1200 liters with a gnerator that puts out 2000 amps at 600volts or anything crazy like that. Compact cars could have a 2 stroke diesel at 1 liter displacement or less to a small generator, midside 1.0-2.0 liters and luxury vehicles 2.0-3.0 liter engines, while light and medium duty trucks could have between a 3 and 5 liter engine, all of these obviously, coupled to a generator chich then powers electric motors attached to the wheels. Even heavy duty trucks (semi's and dump trucks and the like) could benefit from this system... that's why i thought of this in the first place,

Yesterday driving home from school, I saw a semi-truck hauling a railway car of some sort (looked like a rail repair vehicle or something, but its really not that important). The important thing was whatever it was, it was HEAVY! The trailer was sitting 3 inches off the ground at the front, closest to where it connects to the truck, and it actaully scraped the road when the truck took a turn. Now, the point is this truck was stopped at a light when I saw it. When the light turned green, the thing took FOREVER to get going, and make it around its turn. More than half of the time was spent shifting gears! And considering that truck has probably around 20 speeds, that's a waste IMO. Now, as far as i see it, if the truck had been set up like a train locomotive, then it would have gotten to where it needed to go much more quickly and efficiently. Electric motors make their max torque at 0 RPM, so getting moving in the first place wouldnt be a problem, and the diesel engine would be running at *constant* peak torque to drive that generator, in which all of the power would be driving the wheels, while the electric motors themselves would be the transmission, simply speeding up, instead of waiting for a mechanical transmission to shift, bring the engine up to speed, yadda yadda.

So, what do you guys think? Any holes in my train of thought (pun intended

)? I personally thing that the oil corporations have such a tight grip on everyones balls that they'll never allow this to happen on their watch; they're making far too much money off of our inefficient gasloline dependance...

TheSilentChamber · 10-26-2006, 12:16 PM

I'm not sure that you could fit an appropriate sized electric motor at all four wheels (or two wheels) that would be large enough to have any sort of speed without effecting handling out of the car.

Steel · 10-26-2006, 04:16 PM

Then put them in the middle and run axles off of them, like in the current hybrids. Easy problem to overcome. I didn't mean to say that the setup has to be EXACTLY the same as a train. To add to that, since a lot of cars have stop and go driving, have a battery system set up for low speeds where its stop and go to save even more fuel. Use regenerative braking along with the motor to charge the batteries and shazam, ultimate fuel efficiency.

GreyGoose006 · 10-26-2006, 04:18 PM

sure you could.
get rid of the brakes and use large wheels (thats where the trend is going anyway).

you dont need brakes because the other two wheels could have them and the ones with the electric motors could use the electric motor as a brake.

batteries would go in the place of the gas tank. gas woud go under the hood with the small diesel motor. generator would be attached to back of motor like a trans.

think about it. the rear wheels could be driven by electric motors. they would go in place of the diff and be attached directly to the wheel with a few bolts.

if cars were designed a little differently, it would fit very nicely.

Steel · 10-26-2006, 04:27 PM

Well, i'd still want to keep mechanical brakes just in case. If for whatever reason there is a short in the main circuit, those motors are just going to freewheel and not slow you down. Not to mention, once you get under about 10 mph, the motors don't stop you worth a shit.
This design would also be an easy way for every car to have AWD. One motor driving the front wheels, one motor driving the rear wheels. And in case one motor dies for whatever reason, you can still drive.

You could probably fit the battery pack and the fuel tank both in the back. The weight of the diesel motor+a generator is enough so that the car doesnt need any more ballast up front I would imagine.

TheSilentChamber · 10-26-2006, 04:55 PM

I dont know, I'v been around alot of industrial sites in my life and I know that any electric motor to do this sort of thing is going to be massive. I just dont see this being logical. I also dont know if a diesel engine that small is going to be up to the task of making that much power to feed the electric motors. Nothing is 100% efficient so why use A to power B which powers C? Trains use this setup because of the lenth they are dealing with, and the convience of hookup- its easier to hook up a wire then it is to install seperate engines in each one. I'm not saying it cant be done, because obviously it could, but I see no practical reason.

Steel · 10-26-2006, 05:49 PM

Quote:

Originally Posted by TheSilentChamber

I dont know, I'v been around alot of industrial sites in my life and I know that any electric motor to do this sort of thing is going to be massive. I just dont see this being logical. I also dont know if a diesel engine that small is going to be up to the task of making that much power to feed the electric motors. Nothing is 100% efficient so why use A to power B which powers C? Trains use this setup because of the lenth they are dealing with, and the convience of hookup- its easier to hook up a wire then it is to install seperate engines in each one. I'm not saying it cant be done, because obviously it could, but I see no practical reason.

They already have those motors in current hybrid cars. The ones on trains ARE massive, but that's because they need to pull thousands of tons of mass. For a car - 2 tons. Big rig, 40 tons. I dont see why you wouldn't think a small diesel engine could power a car. A current honda 2.2 diesel motors makes 250 torques and 140 horsepower. That's MORE than enough to run that car, and that would be plenty of power to turn a generator. This would translate straight into the electric motors with very little loss. Probably less loss than a typical mechanical drivetrain through a transmission. Keep in mind that the motor i just mentioned is a four-stroke diesel. The torque would be roughly doubled if it was a two-stroke diesel. But since you don't need 500 torques to get an accord going, you could make the engine smaller. Saaay, a 1.3L 2S diesel?

And the reason trains do it is because its much easier to run electric current through cables to motors than it is to drive a 50 speed transmission through 4 to 6 sets of differentials, with the front and rear sets needing to move independantly from each other and the engine body itself. It's also more fuel efficient to run the motor at peak torque and let the electronics and the electrics hand the transmission of the power. That's why these trains only use ~1.5 gallons of fuel per mile when pulling a load. That's pretty damn good if you ask me. Granted, the fact that they are on rails helps a lot with the friction aspect of it, but i'm sure we could see similar gains in the general automotive fleet, and ESPECIALLY the trucking industry, because big rigs are basically road-trains.

GreyGoose006 · 10-26-2006, 06:42 PM

Quote:

Originally Posted by steel

Well, i'd still want to keep mechanical brakes just in case. If for whatever reason there is a short in the main circuit, those motors are just going to freewheel and not slow you down. Not to mention, once you get under about 10 mph, the motors don't stop you worth a shit.
This design would also be an easy way for every car to have AWD. One motor driving the front wheels, one motor driving the rear wheels. And in case one motor dies for whatever reason, you can still drive.

well i said you would have mechanical brakes in the front (where most braking occurs anyway)
i still think that individual motors is best becuase it eliminates all the need for differentials and the like.
i guess inboard brakes are best, and they could be used to recapture energy thru regenerative braking.
this is all really hypothetical anyway...

psychopathicdude · 10-26-2006, 06:42 PM

I've pondered this concept for a while too. Ever since I saw my first Diesel Electric Locomotive powering away from a dead stop without any shifts. Just "BWAAAAAAAAAAAA!!!!!" and the whine from the turbo, of course. Upon researching the means by which the diesel engine is connected to the wheels (or 'trucks', as they are oft referred to as ), I had a "well duh!" moment and wondered why I didn't see this trick setup in any other vehicle.

Especially Big-Rigs. The huge oversize ones might have back-to-back transmissions, with like 30 gears possible. That's insane! And its the very reason why Loco's don't use mechanical transmissions. To handle the torque it takes to get the train moving, and to have the ratio-adjustability to get up to a decent top speed, the transmission might take up another car all its own. Can you say impractical? I knew you could.

Now, why haven't we seen this applied in automobilia? All I know is: "I don't know." But if no one else does it soon, I'm gonna build my own.

GreyGoose006 · 10-26-2006, 06:45 PM

well it surely would be a good idea.
gas IC engines get max efficiency at full throttle.
diesels eliminate the throttle, but i would imagine are more efficient at max load.
of course a turbo is mandatory. lol

Steel · 10-26-2006, 07:18 PM

Quote:

Originally Posted by GreyGoose006

well it surely would be a good idea.
gas IC engines get max efficiency at full throttle.
diesels eliminate the throttle, but i would imagine are more efficient at max load.
of course a turbo is mandatory. lol

Full throttle at peak torque, that is. Same with diesels. It's not mandatory to have turbos on a four stroke diesel, but it helps. It is on a two stroke though.

I personally think have an individual motor per wheel would be a bit excessive. That would really weigh down the car and make the electronics complicated, but then again, it may be the best approach. Who knows, they havent made any cars like this yet.

Hmm. Lets see what the future holds..

curtis73 · 10-26-2006, 07:35 PM

The problem with converting all of your engine's power to electricity is that its INCREDIBLY inefficient. As much as 80% gets lost to heat, light, and sound energies.

The engine itself is only about 87% efficient at getting the energy from the fuel, and then the generator only effectively turns a small fraction of that into electricity

Locomotives use that system mostly because they have to, but its incredibly wasteful. If you were to impliment this in cars you would end up burning many times more fuel to get the same output at the wheels.

Steel · 10-27-2006, 09:26 AM

Even alternators and A/C traction motors?

curtis73 · 10-27-2006, 10:47 AM

Yep. Any time you change states of energy you lose a bunch. No getting around it. In the 80's the big thing was magnetic superconductors that were over 90% efficient, but they still lost up to 10% depending on the transfer protocol. Just getting electricity from the power plant to your house loses over 80% of it, and that's not changing states, its just travelling 20 miles through electric wires.

Even if you made it 99% efficient, you'd still be losing 1%, meaning for the same output to the ground you would theoretically have to burn 1% more fuel in the engine to get it

UncleBob · 10-27-2006, 12:33 PM

there was a automotive college class that made their own diesel hybrid using a VW TDI engine, although I believe they still kept the engine capable of moving the car....although I'm not positive about that....that had rather amazing numbers. Acceleration and mpg.

I've always been mystified why the hybrid craze has yet to see (that I've seen) a diesel engine. Seems rather obvious to me that that would be more effective. I just assumed its something to do with the US' disdain for diesels in cars.

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