Semi Truck Regenerative braking/Electric motor on transaxle could save a lot of fuel 24 hrs per day...

Semi Truck Regenerative braking/Electric motor on transaxle could save a lot of fuel 24 hrs per day...

Truck emissions are a huge contributor to poor air quality, but all electric seems unlikely for heavy trucks for a long time. Even so, electric assist could improve performance while reducing fuel consumption. Heavy trucks waste a lot of fuel climbing hills, braking down hills, and in stop and go traffic. Even large Diesel engines burn a lot of fuel pulling a load to build momentum from a dead stop, and current engine braking and air brakes waste vast amounts of energy during deceleration, especially down hills. In addition, driver cab power needs during down time, when the truck is stopped, unnecessarily burns fuel either by truck engine idling or by an auxiliary motor (Apu).

I'd like to see Tesla Engineers working with truck makers, or maybe with a transaxle make like Meritor, to develop a regenerative braking system and electric motor on the drive axle. When the driver flips on the jake brake, a computer modulates a combination of engine braking and regenerative braking for optimal electrical charge and deceleration.. When the driver steps on the brake, air brakes are assisted by regenerative braking, computer controlled to avoid loss of control even under icy conditions. From a dead stop at a traffic light, for instance, electric motor assistance could improve initial acceleration, and during a hill climb, stored battery charge could boost power by, say, 50 HP.

Currently, DOT regulated drivers are required to take 10 hours rest for every 14 hrs duty, downtime that requires surprising power for sleeper cab habitability and entertainment. Engine idling, which consumes about 1/2 gallon diesel per hour is illegal in CA but remains very routine for many drivers because cab habitability trumps the law during hot and cold weather. Diesel burning APU, small one cylinder auxiliary engines, are much more fuel efficient, but are noisy and really don't provide adequate electrical power to maintain wet cell batteries drained by the array of electrical gadgets, A/C, and kitchen appliances drivers often power in their condo sleeper cabs. None of the current electrical standby systems for trucks cabs provide sufficient electrical power IMHO.

A substantial Toyota Prius sized battery that can provide 10 hours (ideally a full weekend for stranded drivers) AND a source of electrical power for a Tesla sized transaxle mounted motor would be great. Most if not all of the charge for this battery could come from what is now discarded heat on the brake shoes, so service life of drums and shoes would be extended while cab habitation is improved. A combination regenerative brake and electric motor could also reduce fuel consumption because the main diesel motor could be slightly smaller in HP, yet performance would be improved on hills and in heavy traffic.

Eventually, of course, the diesel burning motor would be replaced by fuel cell technology or some other high energy zero emission power source. Next time you drive your 2,000 pound Tesla on the freeway, consider the number of out-of-state 80,000 pound vehicles around you pumping emissions into the air. This is an awesome and growing contribution to global climate change.

Brian H | June 16, 2013

A particularly worthwhile application of regen braking, I wot.

Timo | June 16, 2013

Just commenting: those really huge dump trucks are actually serial hybrids, motors are electric and they use regen to keep steady speed at downhills.

atufft | June 16, 2013

Are you referring to the off-road vehicles used in mining operations? Right, really big diesel to electric conversions are also happening at the shipyards--electric cranes.

But if you look around, big diesel trucks, averaging 5 to 7mph, really need the make over. EGR valves, diesel particulate filters and SCR technology is comparable to what Detroit dreamt in the 1970's when cars had smog pumps. A lot of drivers want to disconnect this junk because it retards performance or is overly expensive to maintain. While the case can be made that instead of building electric vehicles, in many places, like San Francisco, it would be better get folks to simply ride public transit, it's harder to replace the semi-trucks. Trains and box trucks can't fill the demand. Trucks pay for and own the interstate freeway system more than cars.

Also, truck manufacturing is even more component part manufacturer dependent than automobile manufacturing. All big trucks share mostly the same narrow choices of engine, transmission, transaxle, brakes, and so on. So, if Meritor or Eaton developed electric components that really worked, they could easily push market them to big fleets willing to experiment to save fuel, big corp fleets llike Walmart, whose used equipment filters down to owner-operators working the spot market.

Timo | June 17, 2013

I'm not disagreeing. Hybrid makes a lot of sense for big trucks. Also trucks are expensive, so battery price means less in the whole picture, especially if it pays itself back in saved fuel in some timeframe (pulling big truck uphill uses a lot of diesel, better use way more energy efficient electric motors for the extra boost required).

stevehoover | July 10, 2015

Long haul trucks account for 20%+ of carbon emissions from transportation in the U.S.
4-6 miles per gallon of diesel is the average.
One or Two model S motors / controller with a diesel electric generator pack, regen braking and a modest battery pack would no doubt boost efficiency by a significant amount, without being fully electric.

Let's not wait for the battery technology to mature to do this.
Use the superior technology at hand to reduce emissions and help the environment, reduce dependence on imports, create jobs here, lower maintenance / fuel costs and improve profitability for operators,

Think about it, doubling fuel economy for semi's using off the shelf components is huge and not that big of a technical hurdle. A side benefit not lost on marketing.....this would get a big part of the population comfortable with "going electric" when it's technically and economically feasible to do so for the daily driver.

On Guarde

Dramsey | July 11, 2015

But does it make sense? Has anyone actually done the math?

I'd want to see some estimates of how much energy this would actually save, as opposed to a simple "Hybrids are better!" trope.

I suspect the regenerative braking on our Model S cars is much more useful as a single-pedal driving aid than for whatever trivial amount of energy it returns to the battery pack.

Bob.Calvo | July 11, 2015

Here I go again. Tesla is a great company with a whole lot on its plate already.

Ian Wright, a Tesla founder has designed the appropriate balance of batteries, micro-turbine, and regenerative braking to efficiently and more affordably move a vehicle of that size. Wrightspeed provides the drivetrain for retrofitting a vehicle in the class that you are looking at. You can get it a lot sooner this way than waiting for Tesla to get into a completely different slice of the transportation industry. Tesla is already spending more than they are taking in to expand the infrastructure needed to support their current goals.

There is enough room for two visionary companies to help reduce our dependence on foreign oil.

grega | July 12, 2015

@Dramsey, there's plenty of evidence that regen braking is effective for anyone that needs to brake often - but it's dependent on having a good motor (if it can't accelerate at a good rate, it can't stop and regenerate at a good rate either) and a battery that can take the charge.

There a few studies on the extra gain from super capacitors, and claims that the loss is negligible. My quick google searching didn't find studies that pass all my wishes for a study, but that's partly because the studies I found seem to state the obvious (which isn't actually bad), and didn't cover my questions (like cost/benefit).

The surprising thing is that manufacturers like Mazda were backing off hybrids last year because they were getting enough gains in their gasoline technologies. The gasoline engines are getting considerably better, and that will hold back a big switch to BEVs.

For long haul trucks they don't have much braking, so regen won't be as valuable. For garbage trucks they're heavy, don't need to worry about wind resistance/drag (only because they're travelling at slow speed) and stop and start their weight a lot, so regen will be particularly effective. They're also low range over all, so there's potential to be 100% battery... which is where I dislike the wrightspeed goal of small battery with amazingly efficient generator, for local trucks.

I'd rather see the small battery with amazingly efficient generator used for long haul trucks. Less pollution and diesel use is good.

I guess if they're using biodiesel it might be considered totally clean, I'm still undecided on that and need to research it a bit.

Dramsey | July 15, 2015


Let me try again: what I was looking for was numbers.

So say I run a long-haul trucking company, or a garbage service. You come in and tell me that adding electric motors and battery packs recharge by regenerative braking to my trucks will save me lots of money.

1. How much will it cost, per truck, to add this equipment?

2. What is the service lifetime of the equipment?

3. How much does the equipment weight? Every pound of extra weight you add to my trucks is a pound of merchandise or trash that I can't carry.

4. How much diesel fuel will this equipment save me, per 1,000 miles on average?

5. Bearing items #1-#4 in mind, what's the time-to-break-even on this equipment-- i.e. the time when the fuel savings equals the cost of the added equipment? Extra credit: diesel fuel prices are volatile, so a graph showing the different break-even points would be nice.

Without answers to these questions, all you have is idle speculation, which is fun, but that's about all it is.

grega | July 16, 2015

Yes as I said the studies "didn't cover my questions (like cost/benefit)".

Am I right in saying trucks are either long haul or locally based?
ie: trucks don't generally do a combination as much as cars do.?

If so that changes the cost benefit examination significantly too. As I proposed above... a city-based truck has a lot of stop-start movement and slow (no drag) speeds. Where a long haul truck has constant speeds and high drag. So the maths and suitability of each will be significantly different.

At least with long haul you might follow the automobile arguments that are saying advanced engines do better than hybrid options, so without the stop-start traffic the future is better engines and streamlining.

That leaves city-based traffic, supermarket deliveries, garbage trucks etc.

Dramsey | July 17, 2015

So the maths and suitability of each will be significantly different.

Well, of course. What I'm saying is that since you haven't done the math, you have no idea if your idea will actually, you know, least in the sense of saving a significant amount of fuel and thus lower emissions.