I moved this from the other thread as it doesn't quite belong there, but the results from here may get incorporated back into the FAQ.


Heretical mode, or energy re-circulation mode (as Toyota calls it) was discussed in this forum in '07 but more from a technical perspective. See here: https://www.greenhybrid.com/discuss/...al-mode-14215/

I wanted to learn how to trigger it as it can return much higher MPGs than is otherwise possible.

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Browsing through the mileage database came across 'LOL TCH' and a comment he posted on the heretical mode.

From LOL TCH:

Finding that maintaining 1300- 1350 rpm is the quickest route to overdrive. The trick here is to hold 1280 rpm at a constant speed below 52 miles per hour. After a few seconds depress the gas pedal just enough to maintain 1325 rpm. The rpm will drop to about 1150 and current mpg will increase to about 80 mpg. I can now do this at any speed below 52 miles per hour (slightly more with a tail wind), including sub-40 miles per hour. This is a much better choice than using EV mode alone at slow speeds. After all this time I could never really figure out how to reliably get into overdrive. This is the gas pedal manipulation I’ve been trying to find for the past 15 months. Game over, I quit.

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I PM'd him for more info and he kindly added the following:

The trick is in watching the rpm. A SG helped me figure this out but I really don't need it anymore to find that sweet spot. When you're driving at any steady speed below 52 miles per hour (84 km/h) and you're not under any load and are not going down hill, the engine rpm will settle at 1280 rpm. Actually, the engine will settle at 1280 rpm at an even greater speed (up to about 60mph, 97km/h I think), but I can rarely get the car into this sweet spot above 52mph. I just let the engine settle at this speed for maybe a half mile and then very slightly depress the gas pedal. If I'm using my SG, I give the car just enough gas to maintain 1325rpm. The next thing you know your getting out of this world gas mileage. Another interesting thing that happens when you very slightly depress the gas is that the battery charges quickly and to a higher state of charge than you could possibly get otherwise. I've found that pressing the gas pedal just enough to maintain 1325rpm doesn't really increase the speed of the car. It just makes the car sound and feel as if it's lugging. In fact, when I'm not using my SG, I use this "seat of the pants" feeling. It always works. At 40mph (64km/h) I'm cruising at 110mpg and at 52mph (84km/h) I'm getting about 70mpg. One last thing. I usually avoid going into the EV mode. It drains the battery too much. A full battery seems to prolong the cruising distance in the "heretical mode". Let me know if you're able to repeat what I've done. I sometimes think I have a freak of a car since no one else ever talks about this.

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So, does anyone else get into this mode????

 

I will edit the FAQ to include this topic, but I am not sure if I (want to) understand heretical mode.
Can the people who understand it please present it in the form of a simple G & A

The Q is easy..."What is heretical mode and is it somehing that I need to understand?"
The hard part is the answer... Please create a (relatively) easy post that will provide enough information for the average reader to understand, without blowing them away with ultra-high end physics, etc.
Thanks!

 

Okay haroldo, here's my attempt at a Q&A on heretical mode:

Q: What is "Heretical Mode" (also called "Energy Recirculation Mode" by Toyota)?
A: This is an observed mode of operation of Toyota’s hybrids that initially fooled the engineers at the DOE. Because the correct explanation for what was actually happening in this mode was deemed to be so counter-intuitive, it was dubbed "heretical mode" by the community of Prius researchers. Toyota’s name, "energy recirculation mode" gives a clue as to what is going on. Usually, power flows from the ICE to the wheels via two pathways in parallel: (i) the mechanical path through the gears in the Power Split Device (PSD, the planetary gear set); and (ii) the electrical path from Motor-Generator 1 (MG1, which is connected to the PSD) to Motor-Generator 2 (MG2, which is coupled to the wheels). However, if the vehicle is fully warmed up, the high-voltage battery’s state of charge is good, and one is cruising at approximately constant speed on relatively flat ground, Toyota’s engineers realized that they could achieve even greater overall fuel efficiency by operating in an electrically-induced "super overdrive" mode. They do this by using MG1 (powered by MG2, which bleeds off some power that would otherwise go to the wheels) to force down the ICE’s rpm while maintaining approximately the same power output from the ICE (this is known as "lugging" the engine). This drop in the ICE’s rpm moves the engine’s operating point into one of significantly greater efficiency, while at the same time reducing engine noise significantly. The reverse direction of electrical power flow from MG2 to MG1 in this mode is the reason for both the names by which it has become known.

Q: How can you tell when the vehicle switches into heretical mode?
A: One indication can be that the ICE’s rpm suddenly drops substantially (one needs a ScanGauge, or equivalent tool to be able to read the ICE’s rpm), and at the same time the ICE’s instantaneous fuel consumption (in L/100 km as displayed by the FC gauge in metric vehicles) drops dramatically. In US vehicles, the instantaneous fuel economy (in mpg as displayed by the FE gauge) rises dramatically. Engine noise drops at the same time. [It should be noted that similar changes in ICE rpm and FC/FE can also indicate the use of battery assist. In this case an assist arrow will show power flowing from the battery to the wheels. In heretical mode no such arrow appears.] Make sure that the arrow from the ICE to the wheels does appear, as heretical mode only occurs when the ICE is providing power to the car. This said, one should understand the vehicle is often moving in and out of heretical mode quite smoothly and imperceptibly as one drives, as MG1’s direction of rotation changes from positive, through stationary, to negative, or back again. The amount of reverse power flow (i.e., the "extent" of heretical mode, and so the efficiency boost) varies smoothly most of the time, and so the absence of a clear "shift" into super overdrive does not mean that one isn’t in heretical mode.

Q: How can one trigger heretical mode?
A: LOL TCH has made some suggestions, copied in post #1 above. But, the car will automatically take the opportunity to use heretical mode whenever it deems conditions to be suitable. The key is cruising steadily on relatively flat ground. This is all the user has to do. (See the second part of the previous answer.)

Q: How can one confirm that one is in heretical mode?
A: The table given in my post #66 in the thread "Heretical Mode":
https://www.greenhybrid.com/discuss/f49/heretical-mode-14215/index2.html#post147039
will enable those with both a TCH and a ScanGauge to determine approximately when they are in heretical mode. At a given road speed RS, if the ICE’s rpm Ne is below the number given in the table, the car is in heretical mode. I copy the table below for convenience:

RS ; Ne
[km/h] ; [rpm]
50 ; 1019
60 ; 1223
70 ; 1427
80 ; 1630
90 ; 1834
100 ; 2038
110 ; 2242
120 ; 2446
130 ; 2649
140 ; 2853
150 ; 3057
160 ; 3261
170 ; 3465
180 ; 3669
190 ; 3872
200 ; 4076

RS ; Ne
[m p h] ; [rpm]
30 ; 984
40 ; 1312
50 ; 1640
60 ; 1968
70 ; 2296
80 ; 2624
90 ; 2952
100 ; 3280
110 ; 3608
120 ; 3936

Stan

P.S.: Updated tables, with more accurate values, are given in post #6.

 

...thanks!
I'll edit it as soon as admins unlock the thread.

 

Might I add...
Q. How does heretical mode differ from hysterical mode?
A. Hysterical mode is engaged the moment you run out of gas if there is another occupant in the vehicle (typically one's spouse). Once hysterical mode is engaged, the only known method of disengaging is to purchase an item from the local jewelry store. The quantity of hysterical output is exponentially correlated to the length of time you've been married.

 

haroldo — I have modified my tables of values slightly to take into account a more accurate value for the tire's rolling radius (from the Oak Ridge National Laboratory report). The new tables are as follows:

RS ; Ne
[km/h] ; [rpm]
50 ; 1088
60 ; 1306
70 ; 1524
80 ; 1742
90 ; 1959
100 ; 2177
110 ; 2395
120 ; 2612
130 ; 2830
140 ; 3048
150 ; 3265
160 ; 3483
170 ; 3701
180 ; 3919
190 ; 4136
200 ; 4354

RS ; Ne
[m p h] ; [rpm]
30 ; 1051
40 ; 1401
50 ; 1752
60 ; 2102
70 ; 2452
80 ; 2803
90 ; 3153
100 ; 3504
110 ; 3854
120 ; 4204


By the way, the formula relating Ne to RS for the transition between normal and heretical mode is:
3.60 Ne = 78.37 RS [for RS in km/h] = 126.13 RS [for RS in m p h]
and it might be worthwhile including it as well for people who might want to calculate values other than those given in the tables.

I have also added a clarifying comment or two to my Q&A in post #3 above, so if you decide to use this, please use the updated version. Thanks. By the way, I'm open to suggestions regarding this Q&A.

Stan

 

Thanks SPL for the well written FAQ and all your work and discussion in the thread back in '07.

I had thought that the Heretical Mode (HM) was when you saw both arrows in the MDF under low load. Now I will try again to get into the HM hopefully with more consistent results (no SG).

Haraldo: when you are copying SPL's FAQ please add in 'in' to "... often moving **IN** and out of heretical mode" 2/3 of the way through the 2nd Q&A.


Thanks to all!

 

BOFH — Thanks for finding that typo! I've corrected post #3. I'm sure there are other errors too, but I hope not too many.

Stan

 

since I don't understand all of this, can you guys create one post for me to edit in...as it is, there is reference to "in the first post", etc.
thanks!

 

The first post/thread ended up being at a technical/engineering level which is not required in the FAQ, though it could be some fun reading for those that want to know how it all works.

The link is in SPL's post and as long as the forum owners don't purge old messages, the link to it is probably enough.

So to reply to your question/request, use SPL's post from yesterday.