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Comment by ashtonkem | Hacker News Reader

The Prius is the wrong kind of hybrid for that, as the Prius is a parallel hybrid; both the electric and the ICE power train terminate in a planetary gear for shifting power around between the two power sources and the wheels.

What you're looking for is a series hybrid, like the Chevy Volt. In a series hybrid the only thing the ICE powertrain does is run a generator to keep the battery topped up. This allows the ICE to run in its ideal power band range permanently, reducing its size and making gasoline only travel much more efficient while lowering vehicle cost.

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The Chevy Volt is not a series hybrid. It can operate like one, in some modes, but GM actually found, especially for Gen 2, that a mixture of series and parallel is most efficient.

When the Volt runs out of battery, it's almost not noticeable apart from engine noise. The performance characteristics in hybrid mode are almost identical to EV mode in terms of torque/acceleration.

It's an engineering marvel. I love mine. Shame GM killed it.

The 1st generation Chevy Volt works (almost) the same way as a Prius, and does not normally operate the way you've described it. The 2nd gen is similar, but borrows some of the "2-mode hybrid" design from the 2008-2012 Chevy truck transmission (in order to have two gear ratios in electric mode--much more elegant than the Taycan).

Both have a planetary gearset with engine on one gear, output on another, and an electric motor on the third. The difference lies on which gear the second electric motor is placed (motor shaft on the Volt, output shaft on the Prius), as well as some additional clutches and brakes in the Volt.

More info here: https://gm-volt.com/2015/02/20/gen-2-volt-transmission-opera...

Whoops, should’ve gone with the BMW i3 as my comparison vehicle.

And you'll find the Volt outperforms the i3 Rex in terms of hybrid efficiency and performance. When the i3 is in range extended mode it's pokey; and only meant to go a short distance before one gets a charge.

Is that a limitation of series hybrids, or is that a consequence of the engine used in these specific models? The gasoline engine in the 2nd generation volt has 3x the power of the one in the i3 (75kW vs 25kW).

Probably both? I do know that GM ended up going more "parallel" with Gen 2 than with Gen 1. And Gen 2 has more torque than Gen 1, despite switching to a lower displacement engine and going to an Atkinson (tuned for electricity generation) cycle.

Still, though, series hybrids like the Volt and BMW i3 just use regular inline-4 gas engines taken from their other production lines.

The Volt has basically the same engine as in the Chevy Sonic or Cruze, and the i3 range extender option uses the same engine as their C600 series scooters. Those engines are designed with a quick throttle response and a wide power band to operate over an RPM range sufficient to drive a vehicle through a regular transmission.

I don't doubt that for the same time and money, it was far better for GM and BMW to take advantage of the economies of scale around those products than to design an engine specifically to function as a range extender, but if they really took this as a core function or started from scratch I expect they might select a medium-speed industrial diesel engine instead: something optimized for a particular speed and power output that does that one thing optimally.

Same physical components doesn't mean that the injection mapping wasn't customized for the constrained application.

I hope they customized the injection mapping, but the GM LUU engine is still a naturally aspirated gas engine with 10.5:1 compression and 73.4 x 82.6 mm bore/stroke ratio, measurements which primarily came from the ICE-only target applications it was designed for.

Again, completely untrue. A) Volt not a series hybrid B) the gas engine in Gen 2 Volt was not taken from their production line, it is an Atkinson Cycle engine designed for generators, not for their crappy ICE trucks and SUVs.

C'mon, can people research before opining?

"While it shares many parts with the new 1.5L I-4 used in other GM products, the Gen II engine’s combustion process and calibration are specific to the Volt. Its larger displacement not only improves fuel efficiency but also provides more torque, which contributes to the Gen II Volt’s surprising quietness."

https://www.wardsauto.com/engines/gen-ii-chevy-volt-propulsi...

I mean more the target market of the Prius rather than the underlying technology.

Couldn't Toyota have just created another version of the Prius that operated this way?

Or as an add-on trailer.

Tow your own generator.

Thats actually a pretty sweet idea. Only take the generator with you when you need it.

Make them pluggable into the car (vs. towable) and standardize on the interface, and there could be market for renting the generators (like e.g. you do with city bikes - take them from one station, drop off on another).

Attach it to the tow hitch framework like a bike rack. :)

I suspect that would really mess with the load dynamics on most passenger type cars, as the generator would be pretty heavy. I don't think you'd be able to lift a big enough one into the trunk area, and attaching it to the back of the car would be a pain too. I think towing solves a lot of issues for the idea.

That's a really good idea. You typically only need it on long trips, and then it can also be a normal trailer to load all your gear into. Meanwhile when you get to your trip destination, now you have a generator to run electrical devices without having to worry about running down the car's battery.

And it's normally at home, so if the power goes off for a week you can still run your house and charge your car.

This is brilliant.

You should just be able to rent the trailer if you need it a few times a year. Parking space for a trailer that you're never using is going to cost you too much in big cities.

You would need a 20-30kw generator+fast DC charger as the built it AC charger in most electric cars is not fast enough to maintain a charge at highway speeds (especially while towing something).

Like other commentators have mentioned, if a u-haul like network of these were made, if you ran out of charge somewhere, they could drop one of these off to get you going again, as a depleted battery pack will charge slowly, making the van full of batteries potentially more expensive (you would have to pay for an extra 15-30m of their time).

20-30kW might be a bit higher than needed unless the trailer is oversized to provide extra cargo capacity in addition to carrying the generator. You don't need a generator big enough to prevent the battery from draining at all; you just need to extend the range enough to cover a full day of driving while offsetting the extra drag from the trailer. 10-15kW is probably plenty for a trailer that only carries the generator: that would double the highway range of a Model S and would weigh about 700 lbs while being compact enough to have very little aerodynamic drag. A 30kW generator would be enough to double the range even if the trailer doubled the energy consumed per mile, and that's only going to happen with a pretty large trailer.

The Model S is fairy efficient and aerodynamic compared to other EVs.

If anyone did this, they probably would offer 15kW and 30kW versions, so both passenger cars and light trucks would be covered.

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