Posted on 01/21/2007 10:37:35 AM PST by CHUCKfromCAL
I wondered about that too, but then I actually read the article, which says these are not just diesel-electric "hybrids" but hybrids in the Prius sense, with battery-based energy storage.
Sounds like a lot of extra weight to carry around, which would seriously hamper efficiency in hilly terrain.
Saving half of that would be $400M+ in savings per year at current prices. Not insignificant, even to Walmart.
If anything can provide a quick reading on the reliability and true cost of hybrid battery packs, OTR trucking can. They're racking up the miles, day in and day out. It may help push innovation as well.
"Railroads have used Diesel-Electric locomotives for years."
Different concept and requirements.
The electric motor on the drive wheels are used to provide the massive low speed torque needed to start a freight train moving.
I can't imagine how many low gears you would need to do it with diesel alone.
"If anything can provide a quick reading on the reliability and true cost of hybrid battery packs, OTR trucking can. They're racking up the miles, day in and day out. It may help push innovation as well."
Indeed......but the fundamental problem is a big one. For an electric battery pack would have to be big, but more importantly would have to deliver massive currents to an electric assist motor - which would have to be significant to make a difference.
Color me skeptical on this. In rocky mountain states, the battery pack (unless very large) would quickly become exhausted even on some of the not-so-big pulls, resulting in underpowered trucks, with additional weight of dead batteries, crawling even slower than conventional trucks do today over highway mountain passes.
Dennis Weaver wouldn't have any problem outrunning one of these in his Dodge Dart.
Hybrids designs don't like towing things......hard to do an analysis based on what is provided in the article though...
Exactly! I couldn't agree more!
If they had any real regard for the environment and humanity and the Threat Of Global Warming, they would donate this technology to The Third World and America's Poor!
They would also donate their old truck-trailers to The Homeless, and park them in their oversized parking lots, for shelters! Then, they could even PAY the Homeless to retrieve their shopping carts
< /Radical Activist>
Except that he's no longer with us.
Carbon-free society ping.
"Except that he's no longer with us."
....I was making reference to his starring role in the early Speilberg movie "Duel"....a classic!
Not too far into the future Wall-Mart will be marketing their own brand of vehicle, the new WMD, short for the "Wall Mart Driver."
"Wal-Mart Ping" ...if you're around today. :)
What if the setup were really more like a diesel electric locomotive, with the addition of the battery pack to recapture waste energy, from regenerative braking and/or periods of low power demand, such as idling or descending a grade?
PING
"What if the setup were really more like a diesel electric locomotive, with the addition of the battery pack to recapture waste energy, from regenerative braking and/or periods of low power demand, such as idling or descending a grade?"
The problem is how do you store all the energy, not that it isn't possible. There is a tremedous amount of energy to be stored in a loaded truck going downhill.
Diesel Electric would not be practical for a truck, I don't think. It works for trains because of the matter of scale and that the torque curve to get a train moving is more suitable for an electric motor......among other things.
I am skeptical of a hybrid truck, not sure a diesel electric truck would be even practical. need more data....
ROFL
When you can cut the fuel usage of your truck fleet by half you have just saved a tremendous amount of money.
This allows you to drop your prices. (I know that will annoy some people)
Also this kind of thing has tendency to spread. While Wal-mart may lead the way other companies will jump on the band wagon as well.
It would make the use of a smaller displacement diesel engine practical, and fuel tanks could be smaller for comparable range, so some or all of the weight from the battery pack might be offset. Still, since this will be a bespoke design, they'll be looking for weight savings wherever practical and cost effective.. The article referred to "dual mode," so a combination of direct drive and a "reservoir" of recaptured waste energy is what they're talking about, electric assist from reserves in the battery pack for initial acceleration and hills, via computerized sensors of some kind.
"It would make the use of a smaller displacement diesel engine practical, and fuel tanks could be smaller for comparable range"
Ok, here's a little analysis after a bit of research.
Typical max weight for a tractor/trailer is 80,000lbs
Horsepower for a topline Peterbilt is 600hp
Let's assume that to be effective the engine will have to be at least 100hp smaller, representing about a 17% increase in efficiency.
Power density of a Lithium Ion battery is about 160Wh/kg
I'm assuming that accounting for power conversion inefficiency, a 50KWh battery plant will be necessary to accomodate the smaller horsepower - this is enough power to compensate for the 100 HP smaller motor, and keep the Lithium Ion batteries from dipping below the same 70-80% charge rate, that hybrid cars are designed for for max longevity.
This will allow the plant to support 100hp of output for 6 minutes.
This is about 750 lbs of batteries - add packaging, wiring, etc, call it an even 1000 lbs. Add the motors, transmission and other components, say another 1000 lbs.
Add the fact that you'll need to recharge the batteries after they are used, you are reducing payload by 2.5%
all in all the 17% figure is probably gonna be halved - call it 8%.
So for 2000lbs of lower payload, you get a potential 8% increase in efficiency. That may not allow tanks to be too much smaller, but it's nothing to sneeze at over a large fleet of vehicles.
Ok admittedly, it's back-of-the-envelope rough calcs but I can see how this might work. The key is that the additional complexity is reliable enough to not increase acquisition or maintenance costs too much.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.