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Concept: Plug-In Hybrid Drive Retrofit for Heavy-Duty Trucks

The hybrid conversion concept. Click to enlarge.

A pair of Australian inventors have developed a concept for a retrofitted electric drive unit to convert conventional heavy-duty transport vehicles to plug-in hybrids.

The retrofit concept uses a bogie axle drive to create a through-the-road hybrid drive that can reduce fuel consumption up to 25%, by the inventors’s estimates.

This would fast track the introduction of hybrid vehicles onto our roads by utilizing the existing fleet...We expect the conversion unit to pay for itself in the first year of use by way of the reduced fuel consumption. We have secured a patent pending to entice investors so as to start producing this concept.

—Clifford Hall

Main components in the conversion. Click to enlarge.

One mode of conversion is to reverse the positions front to back of a typical two-axle bogie drive unit and to discard the connecting jack shaft. This allows the installation of two electric motors to the former front-drive axle (now in the rear), utilizing the power divider unit.

Converting trucks with a single drive axle and a trailing, non-drive load sharing axle would require either the purchase of another single drive axle to replace the lazy axle or the purchase of a bogie front-drive axle to replicate the other mode of conversion with twin electric motors.

The Halls use UQM HPM150 brushless PM motor/generators for reference. The UQM units offers 150 kW (200 hp) power peak, with peak torque of 650 Nm (480 lb-ft). The inventors envision using a combination of lithium-ion batteries and supercapacitors for optimum performance. The Li-ion pack will be grid-chargeable.

Proposed modes of operation for the hybrid vehicles include:

  • Truck leaves terminal with fully grid-charged batteries.

  • Acceleration using combination diesel and electric assistance.

  • Highway cruising using diesel only and cruise control.

  • Hill climbing, cruise control engages electric assistance to maintain road speed. Diesel rpms and throttle position remain static.

  • Down hill, regenerative braking slows the vehicle and recharges the batteries. Diesel engine rpms remain low, no over revving. Braking also recharges batteries and saves brake wear.

  • Quiet mode, electric assist is engaged to maintain road speed while diesel engine only idles. It is for travelling slowly through towns to reduce noise pollution.

A working prototype has not yet been built.



I've been championing retrofit plug-in hybrids for years. Such a simple way to reduce fossil fuel dependency in the existing fleet....


Go for it! And lets hope the 25% theory holds up in testing.


Go for it! And lets hope the 25% theory holds up in testing.


Why??? PHEVs are best for short-haul urban driving cycles. Heavy trucks log most of their miles in long-haul open highway cycles.

A hybrid retrofit might get them 5-10% by using energy captured while going downhill, but would do nothing for long flat hauls or steady inclines. 25% is a pipe dream. This sounds like a waste.

[q->t to email]


Now line the roof and walls of the trailers with lightweight, thin film solar panels to recharge the hybrid truck's batteries.



Thanks for your input, very positive, the fact that every truck manufacturer and every operator will pay for a system that has break even in less than 3 years and has the chance to reduce fuel costs by maybe an avarage of 15% in the whole lifecycle makes this worth doing.

Not sure why you are stuck in the dark ages, the only way out of where we are is innovation, and this seems like a great way to innovate cheaply


Kevin would you dignify that coment with a reply,surely
you have better hings to do.
REROFIT now thats an adding process so that the regenerative braking gains can be added to other retrofit systems ie westports Deisel ignited LNG.20% and 50% economy and emmisions gains. Using a little utilized or understood fuel LNG. Isay little understood as there seems to be circumstance where LNG is a pollutant in the natural environment, although this may be exasserbated by poor extraction methods. At other times nature leaks all by itself. As with LPG especially when there cannot find an economic value and hence no incentive to ensure containment.
This concept is zero emission compliant and so very desirable. Sydney is planing a whole new freeway to shepperd heavy vehicles out of the urban environment.
Urban pollution, time wasted in traffic snarls ineeficient stop start traffic conditions bring road transport to a standstill and idling vehicles kep pumping out the dirtiest of emmissions are a real technical challenge. The electric hybrid comes into it's own in all of the above. Xtra boost at takeoff where high tourque is really helpfull. Or stop start where Idle off technology (with flywheel pole starter generators,with capacator bleed tech is also retrofit compatable)
These heavy vehichles are loaded with forklifts at large depots, just the place to see palletized battery packs , wich may even be unloaded out of city limits at like Our Roads Transport Authority inspection stations.
Then we see the packs picked up and returned depleted or even charged . By all tose empty lorries The driver happy to backload and acheive a smoother ride.
No more excuse lets get on with it.


The problem with this is its too cheap, uses stock parts can be fitted by any competent operater and oh yeah I really wanted a shiny new one this xmas.

Bill Young

This appears to be a very creative idea. I hope it comes to an economic fruition. It would, of course, help fuel economy more in a stop and go environment but may be cost effective on a hilly crosscountry route.

Roger Pham

Hybrid is great for local trucking to help reduce local air pollution. PM emission is the greatest during diesel engine's acceleration, and the electric motor can help with this. Stop n' go driving and traffic congestion waste a lot of fuel, and hybrid will help this also.

Long-haul trucking can benefit from having the battery pack used to run the accessory load during truck stops, thereby saving fuel and reduce pollution, provide that the battery cost is low enough to make this practical.

Up and down hill driving can do without hybrid, due to the large number of gears (12-18 gear ratios). Down gear shift when going up hill, and higher gear for downhill to accelerate. Most truckers will try to build up speed before an uphill climb, and slow down a little going up the hill, and re-accelerate back to speed going down hill. Hybrid will help more with steeper slopes, wherein you don't want the truck to overspeed too much going downhill nor slowing down too much going uphill.


Roger is spot on. The concept of retrofitting would seem impractical for certain modes of operation proposed by the Halls.

Trucks are hindered by large battery packs when it comes to highway cruising. Also tests with public transit have demonstrated that vehicles are hindered by large battery packs when it comes to hill climbing.

With judicious choice of routes, series hybrid trucks could prove advantageous, just as with buses.


The most effective and cheapest way to significantly reduce Heavy Truck fuel consumption is to improve their ridiculous "aerodynamics" or rather lack of them. Robert Englar's excellent work on this showed the potential for 20% fuel savings or more with cheap plastic and sheet metal fairings. Add on slot blowing/ suction and 50% or more is achievable, taking into account the energy needed for the active pneumatic system. See teh SAE papers Englar has published.

As a hybrid, trucks would surely be best as a series hybrid, with an engine or APU driving a generator to power an electric drive motor. On the motorway, would this not achieve much better fuel economy than the existing direct drive by a large ICE? Otherwise, what size batteries are you going to need? 200kWh? At 70Wh/kg? Even with a truck, that is significant weight not to mention the cost of a Lion "sucker" at that size. Another reason ZnAir is the only viable possibility.

Combine the two - intelligent aerodynamics with series hybrid drive and we start to achieve something useful.


Covering the roof with solar panels.

Assume a 53' trailer 8' wide
~ 39 sq meters
solar energy available 1000 watts per sq meter
~750 watts per hp

~50 hp from an entire roof of a trailer covered with solar cells ... even if they were %100 efficent.

The added weight of the solar cells would reduce the available cargo capacity (axle weight limits) and/or reduce fuel economy.

Real solar cells might only be %20 efficent, and they will not work at peak efficency when they are mounted on a flat roof. The angle of incedence to the sun is never going to be optimal.



Come off your "dark ages" high horse, please. I'm all for innovation where it makes sense, like hybrids in delivery trucks and city buses with frequent stops where regenerative braking will make a big difference. PHEV trucks can also become temporary ZEVs and enter warehouses and other confined spaces or high-population density areas; this is similar to Arnold's point.

But long-haul hybrid trucking is a goofy idea. As Emphyrio pointed out, aerodynamics are a much bigger bang-for-buck, as those losses dominate over long haul routes. I can't see this paying off in ten years for a long haul trucker.

[q->t to email]


Hi kev, like I said , give hese morons the time of day and they pursue you to the grave.


Interesting Just out: International Committe on Climate Change
report 7 years to sort the worst of the inevitabe catastrophic climate change effects. No time to lose and "off the shelf = We can start today.
Adam - why would you poo poo This applicable and available IDEA> get it. is just an Idea, no ones twisting your arm.
This site, to me is a think tank -creative ideas, If you can appreciate it is what its all about.
Real creative Ideas are thin on the ground Please add something possitive.


Cliff your very interesting article re rero ""Heavy vehicle" axles reminds me 1 This applies equally to 4wd rans with P.T.O. as the input.
2 the disadvant ages I see are ! unsprung weight on any vehicle is like bad cholesterol, Ihave no real knowledge of the weight penalty .
3 how would you see the power bought flexibly to the moving diferential.
4 reminds me of an article in the australia and new zealand"Automotive Engineer" describing a Modified Flywheel generator starter BMW @ 1997 +- 5yrs. The modified flywheel / clutch assembly had poles pieces aound the circumference with a stator in bellhousing.
The whole unit added minimuly in the axial or longitudinal dimension and so would be applicable for front wheel drive.
The massive advantage gained from increased diameter would one would think destress the feilds required so minimizing the requirement for fluid cooling.
- Who said that hot water is not desirable etc .
Timing degrees , direction etc are supplied in the usual way with sensors positined on the face. Nowadays,dual clutches are all the rage for constant mesh manual transmissions, so compexity is alaedy the name of the game.
The Integrated controller to switch between the regenerative and starter mode may (in light of advances in technology, Although now well established in tyre balancing and Fisher Price self balancing and load sensing viz weighing wash machines) assist with Transmission vibrations as these could be an issue when mass produced Vis flywheel balancing. This is acheived in the F.P.wasing machine by manipulating the feilds.
If you think about it ,The flywheel and bellhousing in the proving stage would be relatively low tech.
You obviosly appreciate te sense of using existing componentry, with minimal new componentry.
I think (at least in the proving sages, all the systems I have described are similar in tehnical difficulty.
It's already proven in concept and relatively simple to prove in prototype. Just need to assemble the talent.
Arnold Garnsey


Years ago, I had thought of a retrofit for pickup trucks and SUVs, but it did not make economic sense at the time. I would think this would work for local delivery vehicles that log lots of miles though.


I drive a truck for a living.

I'm appalled at what is being said here. It seems that all you people want to do is criticize. Which is ok but it'd be nice if you had any idea about what youre saying.

For example...one guy said

"A hybrid retrofit might get them 5-10% by using energy captured while going downhill," ...."what a waste."

As if that's nothing....not enough to bother.

To date my fuel expense is $40,000 for one truck. I'll take a reduction in cost of 2 to 4 thousand.

And the comments about hills...routes? Nope...no truck driver here.


Those motors look like they would fit inside the wheels... so why not use wheel hub motors? It drives me crazy that people are designing vehicles like this without hub motors! You could put 10 wheel hub motors on the truck in the picture and each would be bigger then the motor they have in the picture! They ICE would only be needed as a range extender just like the GM Volt (EREV).

And to the guy that thinks solar will power a truck... it is 5 watts per square meter not 1000!


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Diesel electric locomotives have been in use for along
time and saved that industry alot of fuel. A big super
capacitor bank would make more sense for the braking
since they can store and then release a large amount of
current and would help big time on the take offs. All
batteries have a certain amount of charge/discharge
cycles and using the capacitors will help the batteries
last longer(which saves$$) IF the motors were optimized
to take the current that a cap can dump without making
the wheel spin or breaking something you could have the
maxumum torque and could even put some ice cars to shame
I experimented with using caps to power toy cars and
if you don't limit the current you will burn up some
brushes/melt windings, but the performance is incredible
and the take off with good traction can't be matched by
any battery. The power to weight ratio of using caps
only on the toy cars makes for a very fast car of course
the range is limited by the amperage stored. I made
them since we were making those co2 powered dragsters
I wanted to challenge my friends with something that
was different and after trying all manner of battery
type from 1/2aaa to those crazy 12volt N batt. I said
to myself capacitor since I remembered the first time I
happened to short out one and was amazed at the amount
of current that was dumped in an instant!! If you want
to experiment those caps from disposable cameras are an
ideal, cheap or free if you ask at the store source for
quick dump capacitors. I even made a small Arc welder
using caps and guitar string and just about anything
else I got my hands on as a kid for the welding rods.
I made some weird pieces and added all kinds of things
onto my Matchbox cars. I had a bunch of Mad max looking
cars that always impressed my friends and everyone
wanted one. I know I know that was a big Non sequitor
but I had to!! Try it you will be amazed at the power
the caps can dump, Of course be careful!!!!!

Paul F. Brooks

How about using capacitors with solar.
You could discharge capacitors into batteries during night time.


Doesn't this still come down to basic laws of physics? F=MA, where the mass we want to move here is up to 129,000 lbs of freight. I'm thinking the power stored in batteries would be dwarfed by that generated by the ICE, and gear box. Decoupling the jack shaft would remove that great force from the rear axle, making the tractor less useful in some cases. I would love to see regenerative braking system that could retrofit existing lighter weight passenger cars. I believe that would save far more fuel than being used in diesel semi fleets, and probably be far more realistic with an appropriate energy to mass ratio.

To the people here who really KNOW something about this subject, not the nay-sayers who just want to criticize: What size electric motors are needed (and how many) to effectively move an OTR Class-8 truck cross country given the varying terrain and conditions? And how much power is needed (electrically) to drive those motors perpetually with a diesel generator?

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