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  #16  
Old 05-01-2005, 12:31 PM
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Triffen,

The reason a Diesel locomotive used an "electric transmission" was that it was impossible to make the necessary 16 speed mechnical transmission. Can you imagine the size and number of gears to handle a 2000HP engine and the problems of shifting the gears. Imagine the drive shafts that would be needed to connect the transmission to the wheels of a locomotive. How big would a clutch or torque converter have to be? How much easier is it to flip electric switches than change gears?


At the time the Diesel engine/electric transmission locomotives came out, they were tripled the fuel efficiency of the steam locomotives, thru the greater efficiency of the Diesel engine. I'm sure the railroads were very happy with than let alone the maintenance that was much easier and more cost efficient on the Diesels locomotives.

P E H
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  #17  
Old 05-01-2005, 12:36 PM
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83-240D,

Aren't all Diesels stratified charge engines?


P E H

Last edited by P.E.Haiges; 05-01-2005 at 08:32 PM.
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  #18  
Old 05-01-2005, 01:52 PM
t walgamuth's Avatar
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hybrids

if i remember correctly from my long ago high school physics class the conversion of electrical to mechanical would be a loss of 10 to30% of the energy. i think that a mechanical transmission would be less than 5% loss.

the honda insight is a standard transmission car with electric assist with a storage battery charged by the motor being activated as a generator under decelleration to charge the storage battery. the prius is an automatic, perhaps a constantly variable type (i'm not sure). having driven both i found the insight with stick, to be engaging to drive and it reminded me of a 240d but faster with a torquey feel. the prius was totally devoid of any feel of control, rather like running a video game.

that said, the type system that the insight has seems a logical derivation of current mechanical and electrical technology that will probably become pretty universal on all vehicles that are driven in stop and go mode... i dont see it being on over the road trucks or road graders where braking is not a big part of the picture.

i am not sure why the train engines all are diesel electric. control? perhaps a rail buff can fill us in on that.
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  #19  
Old 05-01-2005, 02:02 PM
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Quote:
Originally Posted by Triffin
"I'm surprised they don't have a diesel electric combo like a locomotive. A constant speed diesel runs at its most efficient speed driving a generator which supplies power to run an electric motor which moves the vehicle."

I thought of this too .. I think the reason it
isn't done is that you end up with fewer mpg
when the diesel engine is used to run a generator
vs running the drive train .. anyone know for
sure ??

Triff ..
If the engine is disconnected from driving the wheels directly, you will have conversion losses driving the wheels with electricity alone. The automotive hybrids have the electric motor on the same power train, so it can be used as a regenerative brake, and store energy to assist acceleration.

A locomotive is configured the way it is to take advantage of the low rpm torque characteristics of DC motors, and no transmission is then necessary. Think of how many gears would be needed to directly couple a diesel engine to a locomotive -- I ain't gonna clutch that thing!
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  #20  
Old 05-01-2005, 06:34 PM
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Quote:
Originally Posted by Old300D
...The automotive hybrids have the electric motor on the same power train, so it can be used as a regenerative brake, and store energy to assist acceleration.

A locomotive is configured the way it is to take advantage of the low rpm torque characteristics of DC motors, and no transmission is then necessary. Think of how many gears would be needed to directly couple a diesel engine to a locomotive -- I ain't gonna clutch that thing!
Some locomotives do have a form of regenerative brake called Dynamic braking. "The electric current generated by the motors in the dynamic-braking mode is a waste product and is dissipated as heat in banks of resistors located in the locomotive carbody." It's not turned into power the train can use to get moving but it does take massive braking effort off the wheel brakes.

Almost all modern locomotives are now made with AC traction motors (see AC TECHNOLOGY vs. DC HERE )
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  #21  
Old 05-01-2005, 07:04 PM
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Quote:
Originally Posted by 82-300td
Some locomotives do have a form of regenerative brake called Dynamic braking. "The electric current generated by the motors in the dynamic-braking mode is a waste product and is dissipated as heat in banks of resistors located in the locomotive carbody." It's not turned into power the train can use to get moving but it does take massive braking effort off the wheel brakes.

Almost all modern locomotives are now made with AC traction motors (see AC TECHNOLOGY vs. DC HERE )
Aha, dissipating the brake energy in resistor banks as heat is not regenerative braking. Regenerative braking is storing the energy in cap banks or batteries. Locomotives use dissipative braking.
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  #22  
Old 05-01-2005, 08:36 PM
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t walgamuth,

Read reply #16.

P E H
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  #23  
Old 05-01-2005, 09:29 PM
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Ultimate Hybrid ??
Bio-diesel hybrid electric ..

http://hybridiesel.blogspot.com/

still curious thou ..

Would a VW TDI (90hp) engine consume more
fuel per hour @ 60 mph vs running a generator
that was keeping charge on a bank of batteries
of an EV going at the same 60 mph speed ???
Which use would consume less fuel ??

Triff ..
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  #24  
Old 05-01-2005, 09:55 PM
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Quote:
Originally Posted by Triffin
Ultimate Hybrid ??
Bio-diesel hybrid electric ..

http://hybridiesel.blogspot.com/

still curious thou ....

Triff ..
And which would produce less harmful emissions (including manufacture of batteries)
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  #25  
Old 05-01-2005, 10:41 PM
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OK .. you win ..

I'm getting one of these

http://www.primepedalkarts.com/reflex.html

Triff ..
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  #26  
Old 05-02-2005, 12:51 AM
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As "82 300TD" commented, many of the mainline diesel locomotives have what is correctly called Dynamic braking. As was covered there, the braking energy is dissipated in an air cooled resistor grid. True regenerative braking has been used on locomotives, but they were straight electric. In that case when in braking mode the energy is returned to the overhead DC catenary wire and into the distribution system.

One additional system that has had moderate testing in this country but has not been accepted, was use of a diesel engine with hydraulic transmission of the power to the wheels. This system has been used in Europe but did not stand up to the rigors of American raillroading. Units were supplied by ALCo and Krauss Mafei of Germany.
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