Why not diesel electric trucks?

well, there is a reason locomotive use electric traction motors, likely for the level of control and ease of drivetrain accomidation, A pure diesel electric likely wouldn't be as efficient as diesel and conventional drivetrain. And that the electric motors they use develop max torque at 0 rpm and pretty constant torque at very very low rpm, ideal for getting a locomotive moving. And that they can control each drive wheel independently. And with mulitple locomotives in series they don't need to sync the ICE engines, just the electric motors which are orders of magnitude easier to sync.

But why not diesel hybrids? that's what i wonder about. if a diesel 3/4 -1 ton truck had a hybrid system good enough to even capture energy from a in town stop 45mph or so and use it for drive augmentation I suspect it would pick up considerable in town mileage. And add enough battery to capture a a mile or so of downhill when towing, wow, I'd go for that even if it reduced payload moderately.

As far as diesel start/stop I suspect it isn't used much because a diesel is so fuel efficient at idle compared to a gas engine it doesn't buy much.

Electric motors, especially DC motors, can have over 300% torque at ZERO RPM

No ICE's can do that and getting it going from a dead stop requires that. As all ICE's have no torque at zero RPM

Age old discussion and bring this up as an example:

All ICE's use an electric motor to start it because an ICE can NOT develop torque until it gets RPM

Why has it not been scaled down to pull 20-40,000 pounds yet?

Because of this pesky problem.

Trains don't do this for fuel efficiency. They do it for reasons Ben stated. If you have 4 engines pulling a train it would be a nightmare to get all 4 to dump the clutch at the same time! :B

BenK wrote:
Electric motors, especially DC motors, can have over 300% torque at ZERO RPM

No ICE's can do that and getting it going from a dead stop requires that. As all ICE's have no torque at zero RPM

That's why they use a transmission with a clutch or torque converter.

My Hybrid car uses a system much like a diesel-electric locomotive, at low speeds, the ICE engine powers a generator that (along with the battery) powers the electric motor to drive the wheels. At higher speeds, the ICE engine can be coupled to drive the wheels mechanically.

All ICE's use an electric motor to start it because an ICE can NOT develop torque until it gets RPM

While most ICE engines needs some sort of starter motor (not always electric, sometimes air, sometimes a crank, etc), some air start systems inject compressed air into the cylinders to turn the engine for starting so no starter motor required.

But more interestingly, some ICE engines can start with combustion alone, Mazda's Skyactive start/system system knows which cylinder to fire to start the motor by injecting gasoline and firing the spark plug:

https://www.mazda.com/en/innovation/technology/env/i-stop/

But even those have a starter motor for cold starts, and to handle the case where the cylinders didn't stop in the right position for restart.

These guys are trying, but wether they make it….
https://www.hyliion.com/erx-page/

Poor efficiency. Although I would like the idea of skipping the transmission.
Direct connect on the highway and use electric at low speeds around town.
Continue with the electric power boost at speed and regenerative for braking or descending speed control.

I always thought the idea was traction. Steel on steel is pretty slick. Can you imagine what driveshafts would look like if used them to drive all the wheels?
Years back, sitting around a campfire, burning some illegal substances we discussed driving a pump with engine, to power hydraulic motor on each wheel. Would not have the regen of electric, but hydraulic motor lighted than electric, pump lighter than generator. And with valving, the engine could run idle, or most efficient RPM. As speed increase some motors freewheel

Turtle n Peeps wrote:

Why has it not been scaled down to pull 20-40,000 pounds yet?

Because of this pesky problem.

Trains don't do this for fuel efficiency. They do it for reasons Ben stated. If you have 4 engines pulling a train it would be a nightmare to get all 4 to dump the clutch at the same time! :B

This is the reason.

The electric in diesel-electric locomotives is acting exclusively as a transmission.

To build a mechanical transmission capable of absorbing thousands of horsepower and then smoothly meshing it across 4-5 locomotives would be massive, complicated and expensive.

Using a generator and some electronic controls to feed electric motors in place of a transmission is dramatically simpler and allows much easier means of meshing across multiple locomotives.

It's actually slightly less efficient if you compared it to a mechanical transmission once the train is up to speed but getting the train up to speed is a huge issue.

On the other hand for trucks putting our just a few hundred horsepower with no need to mesh with other trucks, a mechanical transmission is comparatively small and simple (keep in mind, simple is a relative term).

JRscooby wrote:
I always thought the idea was traction. Steel on steel is pretty slick. Can you imagine what driveshafts would look like if used them to drive all the wheels?
Years back, sitting around a campfire, burning some illegal substances we discussed driving a pump with engine, to power hydraulic motor on each wheel. Would not have the regen of electric, but hydraulic motor lighted than electric, pump lighter than generator. And with valving, the engine could run idle, or most efficient RPM. As speed increase some motors freewheel

Yes, I can imagine the drive train...look the last steam engines ever built. They were wildly complicated systems of gears, axles and shafts...and even there not all the wheels were powered. Steam engines do have the advantage that they can put out peak torque from zero RPM similar to electric motors.

I believe hydraulic has been used on some smaller railyard engines but it's not as efficient.

There is no "regen" with diesel locomotives. The available power is what the engine is putting out right now. If the engine puts out more power than the electric motors take up, it's wasted but since trains spend 95%+ of their time running at a steady speed, it's not a big deal.

I think the OP was thinking along the lines of a Chevy Volt or Honda Clarity. Use the EV drivetrain, and a diesel engine as a generator. Makes PERFECT sense to me.