Heretical mode on third gen Prius, what do we know?

Whats Going On As I Drive?

Most won't have a clue to your question, until they read THIS page.
Maybe 20 paragraphs down.

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And here I thought it was just the driver who could be a heretic.

 

Only Canadian drivers.

Tom

 

I just learned a heck of a lot! Thank you!

 

+1
..and I thought my car only had 4 wheels spinning...

 

The whole design of the Prius is fascinating in that mechanical complexity has been replaced with software. The software is very complex, but then the bits don't wear out as it spins.

Tom

 

It should as 2010 operates the same. It is also called THS-II (with speed reduction unit).

 

That's a great article (and I had been thinking of thumbscrews and burning at the stake).

"Heretical" mode must happen continuously at highway speeds when torque demands are low (but not zero/coasting). But I notice it most at speeds between 40-60 when the iMPG indicator flickers between 60-80 - showing that the ICE is in fact running but only needing a few wisps of vapor.

This is the most efficient mode, right? (Given that battery-based power is less efficient, and high-torque loads are also.)

 

1) Also see this thread: Introduction to Prius Power Flow.
2) Yes. If it did not, fuel consumption would be higher than Gen II Prius
3) Don't know, never use that screen.
4) I don't think so. In some conditions (at higher cruising speeds), making a very slight change in gas pedal pressure makes a big change in real time fuel consumption; I believe it is related to a shift between normal and energy recirculation mode. You can also easily hear the engine rpm change quickly as it happens.
5) What was the Gen II speed range? Need a ScanGauge to answer and XGauges are not yet available for the Gen III data bus.

 

The "Heretical" (H) mode is basically an "overdrive" mode. It is triggered when the ICE is making more torque than needed. Since Gen III's 1.8l ICE make more torque, it should trigger the H mode more often.

Scangauge II now have the ability to monitor MG1 RPM. Anytime it is in negative RPM, you are in the H mode.

 

I am going to posit that "heretical mode" is why PWR mode is nearly as efficient as (or possibly moreso) than ECO on the Gen III. (NOW who's the heretic? )

Why? Because slower accelleration draws more electric motor power and that electricity has to be put back into the battery by the ICE, which is less efficient than avoiding the battery. Faster accelleration requires more torque and more rpm's (and more fuel) from the ICE, but is still within the 230g/kWh sweet spot (therefore roughly net-zero cost since it takes less time), and (most important) gets you into Heretical mode sooner, where the real efficiency happens (low rpm AND 220g/kWh). And it does that while barely touching the battery (therefore less loss getting up to speed).

It was a different story in the Gen II, for two reasons: a much smaller sweet spot, which was also higher up in the rpm range. So you could be in heretical mode (low rpm), but outside the sweet spot (higher fuel consumption per rpm).

I will further posit that this is why pulse-and-glide is of less benefit in the Gen III - because the sweet spot covers so much more of the lower rpm range than on the Gen II. You don't have to completely shut off the engine to glide because heretical mode will maintain speed at high efficiency, so once you are up to speed, you don't really need to pulse. Again, the Gen II had to pulse to get into the sweet spot, then had to glide (coast with engine off) because lowering the rpm moved it outside the sweet spot and had to be avoided.

This is not to say that ECO is not useful for a downhill drive, where electricity used is recouped by the brakes, but for uphill (and minimal stop&go), PWR should get as good or better results.

End result: a car that can be driven "normally", and still get great mileage. :thumb:

 

It is now available thanks to the great work from this thread.

 

So we just need to look for negative MG1 while ICE is running? I need two scangauges to keep an eye on everything! LOL!

 

Yes, that means MG1 is acting as motor instead of generator. This allows the wheel to spin at high speed while keeping the ICE RPM low. This achieves the "overdrive".

 

So, in the normal mode, the MG1 rotates the same direction as the ICE.
Then, in the heretical mode, the MG1 rotates the opposite direction (negative rotation).
Therefore, there is a transition point where the MG1 rpm becomes 0 rpm at the certain vehicle speed (ring gear rpm) and the ICE rpm combination.

It is known that "MG1 rpm = (ICE rpm X 3.6) - (ring gear rpm X 2.6)".
Then, the zero MG1 rpm condition is "ICE rpm = (ring gear rpm X 2.6) / 3.6".

Following table shows the speed vs ICE rpm combination about the zero MG1 rpm condition.
(note: Gen3 195/65R15 dynamic load tire diameter=615.5mm final ratio=3.267)

	mph	km/h	ring gear rpm	ICE rpm
1	70	113	3172	2291
2	65	105	2945	2127
3	60	97	2719	1963
4	55	89	2492	1800
5	50	80	2266	1636

If you're driving at 60 mph and the ICE is less than 1963 rpm, you're in the heretical mode.

Ken@Japan

 

I don't get a lot of time in my Prius at high speed, but isn't it in this mode a lot of time? I seem to recall RPM's less than 19xx a lot of the time at 60mph.

Can't wait to check it out with the new MG1/MG2 Xgauge's

 

Could it be the reason why you feel a slight jolt when transitioning between coasting at high speed and moving under power? MG1 changing direction?

 

I have been wondering for some time if MG1 could be stopped (zero RPM) while MG2 and the ICE are spinning. Now you give me the opportunity to ask the following question: Since MG1 has to draw torque from the ICE (as per the PSD), can it really stay at zero RPM? Is zero RPM for MG1 only a transitional state when the ICE and MG2 are spinning?