h a l f b a k e r yOn the one hand, true. On the other hand, bollocks.
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Large goods vehicles have problems when road conditions are poor.
This is because the propulsion comes through just two axles on the tractor unit; the rest of the axles are "dead".
If such a vehicle were built as a Diesel-electric battery hybrid, all wheels could be powered as the problem of transferring
energy from the tractor unit to the trailer requires only a suitable cable.
Part of the battery capacity could be located in the trailer, giving better mass distribution when empty and reducing the size of the connecting cable.
Regenerative braking would recover energy efficiently rather than dissipating it as heat.
Acceleration would be improved as the powerplant only needs sufficient capacity to keep the battery charged when cruising, surge demand for starting from rest being met by the stored energy in the battery.
Wanted category: Vehicle:Goods or Vehicle:Truck or similar.
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There's plenty of people hawking hybrid trucks around the
globe, but they're nothing like this. As far as I can tell,
even the major manufacturers are pushing conservative
mild paralell hybrids. Which is mainly for marketing I
assume. |
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You're proposing a serial hybrid. Essentially internal
combustion engine (ICE) > generator, generator >
propulsion motors with a battery buffering the difference
between supply and demand of the drive train. Great,
works for locomotives & submarines. You get to throw out
the gearbox, optimize the ICE to a specific output and
play around with the traditional layout. |
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Adding drive to the trailer would be unpopular I think,
truck drivers start sweating when the trailer starts
pushing. I'd stick with making a better tractor, and stay
versatile regarding what can be pulled. Tractor all wheel
drive is already widely available if you want to pay for it,
locking diffs and all. Logging & mining have been dealing
with poor/no road conditions for some time, months
possibly. A single-axle drive truck sliding down an icy hill
in Yorkshire is a symptom of insufficient box ticking at
purchase, not availability. |
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But, you could make a compact low CG chassis with a
clever drive train. Hide an ICE, say a small turbocharged
LPG engine in the middle. Plug-in charging and regen
braking don't have nearly the same benefits as, say a bus
though. The percentage of plug-in energy to total trip
energy would be tiny, stop-start component is minimal.
Same with the generator, you get to optimize to a
specific power output, but truck diesels are already doing
that, hence the 10-30 gear ratios. |
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I think the low hanging fruit for truck efficiency is finding
a way to mitigate the wake induced drag. I'd go with
blown flaps on the bottom and sides of the trailer fed by
an auxillary turbo. |
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There's no "electric vehicle" category either, or
"chicken powered helicopter". In fact the entire
vehicle listing needs to be enlarged |
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// the entire vehicle listing needs to be enlarged // |
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Send in the Panzers ... carve out some Lebensraum. |
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Piston engines are fine for mechanical drive; being able
to change engine speed quickly is an advantage.<but>
But they are horribly inefficient.
If you're building a "series" hybrid, it's far better to use a
turbine (gas or otherwise; I've see a test-bed turbine
running on powdered coal...). It just sits at optimum
efficiency, pumping out electricity. Although they are
more complex and harder to maintain...
As for the idea, yes! Although as [bs0u0155] mentioned,
probably not the powered trailer (although they do exist,
too). |
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// they are more complex and harder to maintain...// |
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We would dispute the complexity part, for non-aviation units. The maintainance requirements are variable. |
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There's no benefit to gas turbines in terms of fuel
efficiency in this application. Sure, they're smaller
and lighter, but that's not critical here. Apart from the
build tolerances, maintenance costs and fuel
fussyness, you also have to get the power out of a
super high rpm floating shaft and gear it down. Each
(3?) step costs you ~10%, on the way to the
generator. That's what kills you. |
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I thought what killed you was an uncontained blade failure? |
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Depends what you're standing behind. Wear your kevlar with pride ... |
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// no benefit to gas turbines in terms of fuel efficiency // |
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Maybe not efficiency - but they will run on very low grade fuels. OK, maybe not Bunker A, but certainly a lot less demanding than regular automotive diesel. Unrefined vegetable oil, long chain paraffins, whatever will fit through the injector nozzle ... |
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It's amusing to realize that governments are running scared from the development of practical automotive turbine hybrids in passenger cars - since they will run on virtually any hydrocarbon, it becomes incredibly hard to tax the fuel, if users choose to "extend" their diesel or jet kerosene with untaxed products. |
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// truck drivers start sweating when the trailer starts pushing. I'd stick with making a better tractor, and stay versatile regarding what can be pulled. Tractor all wheel drive is already widely available if you want to pay for it, locking diffs and all. Logging & mining have been dealing with poor/no road conditions for some time, months possibly.// |
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This is intended for exactly those poor surface conditions, as found (for example) on the Coquihalla Pass in some seasons. The trailer doesn't need to push that hard; the traction control will handle that, as will the antilock/antiskid regenerative braking. |
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All-wheel power has made a tremendous difference to rail vehicles. |
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Also, we have looked closely at the category Vehicle:General and consider it disappointing, indeed unsatisfactory; there are no flags on it, nor is there an escort of armed motorcycle outriders. And it needs to be painted olive drab. |
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I think storing the fuel source within the truck is a massive source of inefficiency. A better approach would be to have one lane of a motorway rigged with overhead power cables, and every heavy goods vehicle to pick up power from these cables with a roof-mounted pantograph. Then, every one of these vehicles in the country would be powered by a single small power station. |
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You could reduce tyre wear and road maintenance by replacing the road surface with long strips of hard metal that the vehicles roll on. With all wheels powered, gradients would be less of a problem, and there could be drop-down rubber tyred wheels - or a cog system - for steeper hills; the driver wouldn't have to steer ... there's no end to the possible benefits. |
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This thing would be stupid heavy and difficult to
package enough battery to do the job. |
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But it’s a hybrid - it doesn’t need huge batteries |
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The mass of the generator, battery(ies) and motors is offset by the lack of gearbox, differential and other final drive components. |
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The cost of the chassis needs to be compared with the cost of dropping a conventional vehicle and payload down a ten metre high bank into the trees ... |
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//This thing would be stupid heavy and difficult to
package enough battery to do the job// |
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//But it’s a hybrid - it doesn’t need huge batteries// |
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I think we forget that cars/trucks are already hybrids.
Almost all of the functions we rely upon in a modern
vehicle are electrical, powered by a generator mounted
to the engine using a battery to smooth out the supply-
demand mismatches. A serial hybrid simply moves one
more system, the propulsion to the electrical side.
Granted, it can be a real energy hog, so you need a larger
generator, but conceptually it is only a slight shift. |
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As for battery packaging and size, well a truck of say 15
tons needs about 600kJ to go from 0-50mph in a fairly
sprightly 10s. You can store that much energy in ~2kg of
lithium ion battery. Admittedly, there will be losses in
wiring, speed controllers and motors and getting energy
like that out of small batteries kills them, but it's all very
doable. |
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One drawback I thought of regards the one motor per
wheel thing. Traditional transmissions that drive many
wheels* usually have a way of managing the torque,
locking differentials for example. That's because in poor
conditions, it's not that wheels lose traction, more that
some wheels have all the traction and you need to get
the torque to those. So with locking diffs, you can bring
the full engine torque to say 2/8 wheels. Now, with single
motors per wheel, you'd only have 2/8 of the total torque
available to wheels with traction. Is that going to be
enough? |
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*I would have said "all wheel drive" but that's a specific
term that implies center differentials, they need to
organize the nomenclature, I blame marketing. |
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Yeah, and the sales guys ... bastards, all of them. |
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// ~2kg of lithium ion battery. // |
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Just one conventional differential/axle assembly is a couple of hundred kilos at least - save on that mass, and throw on a 100kg LiIon battery, and you're still ahead. |
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It's probably safe to assume that the mass of the generator pretty much cancels out the mass of the gearbox; the control electronics don't weigh that much. |
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//you'd only have 2/8 of the total torque available to wheels with traction // |
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Not necessarily. Motors can run at substantial overloads for short bursts without harm - particularly if they're being driven by a smart inverter with temperature monitoring. The system boosts power to the non-slipping wheels until slip is detected, then backs off. If the other wheels still don't catch (though you're hopefully still moving in the desired direction, so they might) and the motor's getting too hot, then you stop. Not good, but better than a skid. |
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//Just one conventional differential/axle assembly is a couple of hundred kilos at least - save on that mass, and throw on a 100kg LiIon battery, and you're still ahead.//
This raises the valid point that, given that many parts of trucks are heavy, and also that batteries are heavy, there is a weight saving to be made by creating a battery in the same shape as these heavy truck parts. E.g. the chassis, axles and wheels are heavy, but if these parts were made of batteries instead of steel the truck would be more efficient. I know people are going to complain that lithium isn't as strong as steel but I'm sure these minor problems can be overcome. |
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"That battery isn't going in my tunnel, it's flammable!" |
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"Not just flammable, load bearing and flammable!" |
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