WannaBeZ28

For those who don't know a typical diesel locomotive engine has a main diesel engine which once turned up to full power stays there and just runs a generator. The generator then powers traction motors on each axle.

I was thinking with all the hybrid vehicles coming out why has noone thought of doing it this way? I can't imagin you would need all that strong of an engine to run the generator.

You would also not need a transmission as electric motors can produce torque at pretty much any RPM.

So whats wrong with this design?

Ken S

seems like another unnecesary energy transformation step - another step to lose energy... why not just drive the wheels directly by the diesel engine?

R377

It's certainly been considered before, but two problems are cost and efficiency.

Anytime you convert energy from one form to another you lose a little (or a lot) of it. By having the IC engine power a generator which in turn spins the electric motors, you are losing (I would guess) about 20-25% of the power produced at the flywheel by the IC engine. Some of that loss is negated by not having a transmission, and by optimizing the IC engine to run at a constant speed, but on the whole I think it's a less efficient setup. That's why Honda and Toyota hybrids have setups that allow the IC engine to directly drive the wheels.

Cost is high too, because you need an IC engine, a generator, batteries, motors, and controllers. While much of this is required for a setup like Toyota's hybrids too, in this case the generators and motors have to be much larger and heavier because they are now doing all of the work instead of just pitching in when needed.

Locomotives use this setup mainly because it's an easier way to get the power to the ground, especially at low speeds when pulling a heavy load. Designing a transmission that would allow the full 6000 HP to be put to the ground at 1 rpm, and yet still reach speeds of 60mph +, would be a daunting task. Packaging would be tougher too, trying to get mechanical power to 6 drive axles over the length of a locomotive chassis.

I know that the GM Powertrain hybrid engineers have talked with GM EMD (the division that builds GM's locomotives), but I don't think they ended up having a lot to share.

WERM

See the explanation above from R377. The locomotive example is what is known as a Series Hybrid (Think on board generator) It is usually a more complex and expensive system than a Parallel Hybrid (Think electric supercharger) and is what Toyota and Honda use.

When I was in college, I was part of a team that built a Dodge Intrepid hybrid (series hybrid) that was powered by a souped up Geo Metro engine. It was nearly as quick as a standard intrepid.

WannaBeZ28

Well.. Good enough for me!