Comment by mschuster91 | Hacker News Reader

Comment by mschuster91 | Hacker News Reader

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> The ideal drivetrain was invented over 20 years ago by Toyota and apparently nobody but me and Honda noticed it!

The problem is hybrid drivetrains are complex. You don't save anything on the complexity of a combustion engine and exhaust train (over 1000 individual parts that have to be machined at extremely low tolerances), but add a more complex transmission (it needs to be able to work with two distinct inputs) and an electric drivetrain on top of that.

It is worth it in terms of energy efficiency and acceleration stats since even a small electric motor can supply a lot of torque at low speeds until the high-horsepower combustion engine catches up (virtually all modern cars have a turbocharger that needs time to spin up), but it's technically challenging to actually build into a modern car design - unlike 90s cars with ample space available to stuff components in, in a modern car every cubic centimeter is accounted for due to crash resistance.

As a simple driver of cars, I've never understood why no one has mass produced an EV with a built-in generator. That would avoid the complexity of the hybrid drive train, allow easy plugin and short range electric-only travel, and could even be offered as an optional attachment. So what am I missing? Is the efficiency gained by the generator offset by losses through the EV system?

This was the GM Volt, predecessor to the Bolt: https://en.wikipedia.org/wiki/Chevrolet_Volt GM ceased production in 2019. The answer to your question can probably be found there, but IIRC [from GM's perspective] the consumer market preferred ICE + battery over electric + generator, especially after the all-electric options came to market and siphoned demand from the latter.

BMW i3 and Chevrolet Volt both had that option: https://en.wikipedia.org/wiki/Range_extender

And of course, there are plug-in hybrids: https://en.wikipedia.org/wiki/Plug-in_hybrid

It just turns out not to be worth it. The generator is a lot of weight to add, and a whole bunch of new parts to maintain.

It's a lot easier to add enough batteries to match the range of an ICE car. Range anxiety is largely manufactured at this point. The cars know how far they can go and where the chargers are. A gasoline powered generator would be a huge extra cost with no real upside other than averting a non-problem.

Edison Motors is working on a system like this. They're looking to sell kits for retrofitting it onto pickup trucks, & a larger scale semi truck cab version for use with logging trucks. It looks great in their videos, although I'm not sure if they're selling to the public yet - probably a ways to go before it's really mass produced.

That is called a series hybrid and the reason they're not popular is that the power split device in common hybrids is simply better.

The power split device isn't an ordinary transmission, it's a set of planetary gears with a fixed gear ratio between three shafts. One goes to the wheels, the other two to the engine and the electric motor respectively. The ratio of the engine speed to the wheel speed is then set by the speed of the electric motor connected to the third shaft, which gives you a CVT with no belts, clutches, torque converters or even synchros.

The transmission is "more complicated" only in the sense that it contains electric motors. In every other respect it's simpler, more efficient and more reliable than an ordinary transmission. Meanwhile those electric motors mean you don't need a starter motor or an alternator because the engine can be started by the electric motor through the transmission and an electric motor is a generator when operated in reverse.

A series hybrid still requires you to have a gas engine with all that entails, but now the gas engine needs its own dedicated electric generator/motor and you can't deliver power from the gas engine directly to the wheels, so the traction motors have to be bigger in order to supply 100% of the torque used in acceleration instead of the gas engine and electric motors both contributing. That makes series hybrids heavier, slower and more expensive, so they're basically useless. Probably the main advantage would be that you could offer the generator as an option on what would otherwise be a full electric vehicle and then only people who need the extra range would pay for it.

Wouldn't an additional advantage of series hybrids be that the engine can be tuned to operate solely in it's most efficient RPM band, since it just charging the battery and doesn't need to deal with changing speeds? This can (according to some very cursory googling), result in efficiency gains of 20-30% relative to the least efficient RPMs. This should at least partially offset some of the size and weight considerations, since you don't need to size the engine for it's energy output in less efficient speeds. This seems like it would be most important in stop-and-go conditions where the engine is spending considerable time at less efficient speeds, such as in a bus.

The parallel hybrids can already do that because of the CVT.

In practice they also allow the engine to run at higher speeds under heavy acceleration because the peak efficiency RPM and the peak power RPM are different and the assumption is that if the driver is stomping on the accelerator they want to resolve the power/efficiency trade off in favor of power right now, which is another thing the series hybrids can't do.

Ram is trying to commercialize this in the form of the Ramcharger. I don't know if it will succeed.

Most BYD PHEVs work like that - with the additional option of connecting the engine directly to the wheels via a clutch at highway speeds. I think Honda has a similar system.

You're talking about PHEVs, basically. Ramcharger is an example of one where the ICE engine only charges the battery; it's not connected to the drivetrain.

The BMW i3 had this as an option; I don’t think it was a particularly popular option.

I know people have already said that PHEVs do this, but the other comments made it seem more niche than it really is... About 35% of EVs are like this: https://en.wikipedia.org/wiki/Plug-in_hybrid#/media/File:Rat...

Some hybrid drivetrains have fewer moving parts than a traditional ICE and are more reliable.

That undersells it. The data on hybrid drivetrains is pretty clear--it's definitely more reliable. Even mechanics will tell you that; certainly mine did, and he's not a masochist. Start+stop is hell on mechanical drivetrains. It's a no-brainer when purchasing a new car except that there's still a premium for hybrid, so the RoI might not be there given baseline reliability and depending on your preferences. Though the premium gap is closing, at least for non-plugin hybrids. Plugin hybrids are the new premium option in model lineups, so traditional hybrids are moving down market.

My plugin hybrid (I just bought it 2 weeks ago) is on track to save me $200/month over the others similar vehicle it replaced (minivan with the same engine, but 10 years difference in years, so lots of other differences).

My ROI is in how I can slam in reverse when I'm rolling forward or floor it whenever without concern for the drivetrain.

Sounds counterintuitive.

Any references?

https://www.rav4world.com/threads/how-the-ecvt-operates-with...

At least for Toyota hybrids, the intuition is that the traditional ICE transmission system is replaced by what Toyota calls a "power split device" which continuously feeds and balances the electric and combustion power sources. This power split device uses a simpler gearing system (enabled by the high torque electric motors) and appears to be mechanically simpler and more reliable than traditional transmission systems (which probably wear out quicker than the engine in most ICEs).

> virtually all modern cars have a turbocharger

This is not really true in the US, but maybe moreso in Europe, where engine displacement is penalized?

> that needs time to spin up

Porsche's latest 911 does something very cute here ("T-Hybrid"): they have a small electric motor in the turbo. They use the high-voltage hybrid battery to rapidly spin up the turbo on demand to significantly reduce turbo lag (one of the major drawbacks of a turbo engine). Then, at lower load, they can also regen the battery using the exhaust gases and that same motor.

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