How does power add up in a Toyota hybrid?

[raubvogel]

I wonder what made them change. From your diagram it looks closer to the Toyota system but still able to allow you to run directly off the engine. In other words, it leads itself to more combined power at the wheels than the Toyota system.

[Vman455]

Originally Posted by raubvogel

211 + 167 - 68 = 310 which is greater than the 272PS mentioned in https://blog.lexus.co.uk/history-lexus-hybrid-drive/. Where are the 41 horses?

The gas engine and electric motors don't reach peak power at the same rotational speeds or road speed.

[Ecky]

Originally Posted by raubvogel

I wonder what made them change. From your diagram it looks closer to the Toyota system but still able to allow you to run directly off the engine. In other words, it leads itself to more combined power at the wheels than the Toyota system.

My guess, the new system is far lighter and more simple than both their old system and Toyota's. Honda's new system allows the car to drive on electricity alone, and to toggle the gas engine on and off while keeping the car in motion. The old IMA system required the gasoline engine to always be spinning while the car was moving forward, which caused a need for Honda to build some complex valve and cylinder deactivation systems for the engines in their hybrids. And unlike Toyota's system, there is no large and heavy planetary gear system. It's just an electric motor directly driving the wheels, and a clutch that can connect the gas engine in parallel with a single speed reduction. Compared with a 6 speed manual, which has approximately 17 actual gears and pinions in it, this one has 2 (or possibly 4 if the electric motor has a reduction).

Toyota's planetary gears are a more flexible system that allows more combinations of output and input from engine and electric motors. The gearbox is not *that* large (it's still smaller and more simple than traditional transmissions), but it's relatively much larger and heavier than Honda's new one. It also requires the electric motors to be spinning and pulling power from the engine at certain road speeds and loads. Sometimes one motor needs to be pulling power from the engine to spin the other motor faster, to lower or raise engine RPM. Converting from mechanical to electrical to mechanical is an efficiency loss.

Driving the wheels directly from the gasoline engine is more efficient, so long as you can keep load and RPM within its island of peak efficiency. That's how the original Insight was able to see 100mpg+ at certain highway speeds, but had such a huge gap between city and highway RPM. Toyota's system by contrast brings up the average system efficiency tremendously (city mpg sees a huge increase) at the expense of peak efficiency.

All 3 systems have pretty major compromises. GM and Ford have both used systems similar to Honda's original IMA, and Toyota's planetary gears. I *think* Honda's new system is still unique in a production car.

[cRiPpLe_rOoStEr]

Originally Posted by Vman455

The gas engine and electric motors don't reach peak power at the same rotational speeds or road speed.

That's also a good point. IIRC the electric motors are optimized to improve the low-end performance in order to compensate for the lack of a more conventional transmission.

[raubvogel]

I have to say from your diagram and explanation the new Honda system is much better than the Toyota one, which seems to be more electric-centric. Is it derived from the NSX one?

[Ecky]

Originally Posted by raubvogel

I have to say from your diagram and explanation the new Honda system is much better than the Toyota one, which seems to be more electric-centric. Is it derived from the NSX one?

I haven't actually looked too closely at the NSX system! It might be difficult to find info on it.

The problems with the Honda system are that 1) The electric motor is solely responsible for propelling the car below 60mph, so you need a pretty large electric motor (there's no "assist"), and 2) the gasoline engine can't send power directly to the wheels below 60mph, meaning you *always* have a double conversion loss from mechanical to electrical, then back to mechanical energy. Not a big issue for city driving because most of the losses are from stop and go, but steady-state driving could be more efficient with Toyota's system.

[raubvogel]

However, in the Toyota system your engine is limited by what MG1 can handle. If there was a way to lock the planet gears (engine) to the outer ring gear (wheel + MG2), things would be much more interesting.

[hayden55]

For the most part it is this:
1. The gasoline engine produces very little torque off idle, peaks at 4000 rpm and then tapers off to redline, and the horsepower of the gasoline engine increases from idle to redline at about 5200 rpm.
2. MG1 is the three-phase starting motor that starts the gas engine and is also an alternator.
3. MG2 is the main three-phase electric output motor and can also be an alternator.

The electric motors have peak starting torque at zero rpm and decrease all the way up to max rated rpm of each electric motor depending on design parameters. Rated peak power output (not at max rated rpm of each electric motor) is somewhere in between where efficiency, emf back and forth, and amperage create the highest power output. Also the electric motors are probably rated for a peak rating of 60kW (basically the max heat rating it could produce) but the rest of the system can't support it so it'll only produce as many kWh as the inverter and battery will let it suck (bottleneck).
Kinda like saying a gasoline motor is rated for 350hp but we are going to put a 200hp fuel system on it to lower its output to 200hp.
More than likely they chose this motor system as it was the most efficient system for overall driving and it was easier to find an inverter to match the starting torque of the little motor, and then start the next big boy electric motor when its already spinning (less starting torque to overcome which requires smaller inverters/and less amps). City driving nets them the highest points with the EPA rating system (55% city) and focusing on highway doesn't get them as many points for their corporate mpg average.
Similar story: we were given a three-phase motor but couldn't afford a big enough inverter to overcome locked rotor torque/starting torque to start the motor so we swapped to a DC motor.
The max discharge limit of the Gen 3 Prius' battery was only 27 ish kW which is about 36hp peak that the battery is rated to sustain (its sustained power output rating or also its sustained heat output rating without overheating the battery).
So it looks like the battery was the limiting factor for system power output, but the electric motors and gasoline engine create fantastic avhp and avtq together (flat/er hp and torque curve) over the operating range with the CVT than seperate for increasing speed, gives up peak efficiency on steady state cruising from all the conversion losses but tries to make it up by staying in peak BSFC better, and from having a smaller gasoline engine than normally required, and trying to shut off the gasoline engine as much as possible at slow speed.
Basically if you were a car nut and put in a big ass battery and matching inverter the electric motor is rated to sustain and net you up to 60kW more horsepower (80ish hp). This can contribute to peak system horsepower if they are geared to achieve peak power at the same rpm (which they aren’t).

So 98hp plus about 36 ish horsepower = 134hp

https://ebikes.ca/learn/power-ratings.html