[em500]

So this is specifically about Toyota's hybrid engines (which is very different from e.g. Honda's engine, not to mention plug-in hybrids or "mild hybrids"). The explanation of the mechanics starts around the 36 minute mark.

I always found most explanations of Toyota's Power Split Device too abstract, until I found this page where you can play with the sliders to see how the power is actually split between the ICE and the MG1/MG2 electric generators: https://eahart.com/prius/psd/

[javawizard]

Fun story: I used to own a Prius, and it turns out they expose the speeds and torque values of MG1, MG2, and the engine independently on the OBDII port.

What this means it that you can set up an app like Torque[0] and add widgets that show you how fast each of the motors are spinning, live, and watch what happens when e.g. the engine starts: MG1 and MG2 both torque the engine forward, MG2 just enough to stop the car from attempting to roll backward in response to MG1's torque through the planetary gearset, and then MG1 spins up with the engine and then stops torquing it once the engine reaches idle.

Battery charging while idling is similar: MG1 turns itself into a generator, fighting the engine and generating electricity in the process. The throttle opens considerably, as if you'd pressed the accelerator halfway to the floor, but MG1 and the engine work together to keep the engine's RPM around ~1,200 so you'd never know it - it's as if you're driving up a really steep hill that stops you from accelerating even though you have the gas pressed halfway down. And then MG2 torques backward to stop the car from rolling forward any more than the Prius's normal "simulate a normal gas car's tendency to roll forward when the user lets their foot off the brake" would have it do.

It was fascinating to watch, and I kind of regret not building an app similar to the parent comment's link that showed what my car was doing in real time with the gears drawn out like that.

[0]: https://torque-bhp.com/

[redwall_hp]

The Prius model is basically how the new Honda hybrid power train works. (I'm gearing up to buy a new Civic once my insurance gets me my payout.) It has a two motor system (traction and generator) coupled to an Atkinson cycle engine with a planetary gearbox.

However, it's a 2L engine and the whole thing puts down 200hp, netting acceleration that beats a Civic SI and ~50 miles per gallon.

They first trialed it in Japan and Europe as the Civic EHEV a few years ago, and as of 2025 it has replaced the Sport and Sport Touring trims' former turbocharged 1.5L power train.

[red369]

Hmm - I’m not an expert on this, but I thought the e:HEV system was quite different.

More like an engine connected to a single very long gear (like top gear), to avoid converting from physical motion to electricity and back to physical motion, at motorway speeds. And also a clutch, to disconnect that system completely, in which case the combustion engine can drive a generator, and send electricity to another motor driving the wheels. Plus there’s a battery involved, and the motors can assist or regen when the physical drivetrain is connected.

It’s all very cool, and I expect even more efficient than the Toyota system on the open road, but a little less during city driving. I can go into why I think that, but I’m not even sure I’m right :)

https://global.honda/en/tech/two_motor_hybrid_system_honda_e...

Edit: I just wanted to add, that Civic with this drivetrain always seemed like a good choice.

I’ve tried to test-drive a Honda with this setup twice. Once the dealer misunderstood me and I drove some boring mild-hybrid CVT Insight or something. I would have even been happy trying out the dual-clutch hybrid they were using in some models then. I’d already driven their mild hybrid a few times. It got good mileage, but not as good as Toyota’s system, and didn’t have anything else going for it. The second time I hadn’t realised that they didn’t even bring this Civic into the country. We drove the regular CVT anyway, but it was a huge disappointment, knowing other countries had the e:HEV.

2nd edit: I incorrectly called the combustion engine “the motor”, which is something I do all the time, but need to avoid when talking about hybrids

[red369]

Just in case, this video has more detail than you're likely to want on how the E:HEV works:

https://www.youtube.com/watch?v=QLUIExAnNcE

[consp]

Note that Ford's plugin hybrids (using the same 2.5L engine as the full hybrids) also use the same technology (due to them having a cooperation and patent sharing agreement with Toyota) though they do differ a tiny bit due to the engine.

The tool is interesting though the Ford system can run independently on MG2/MG1 alone up to about 130kph (~80mph) depending on requested torque and load.

Only thing Ford screwed up is the battery (or Samsung since this time it's the cells).