Glide vs Heretical: what is the difference?

There's a "one of these things is not like the others" going on here.

Most of the things in that list are driver techniques, things you can select or choose doing or not doing as the driver.

"Heretical mode" isn't a driver technique, it's just a cute name for the overdrive mode of the transmission, so called because of the slightly mind-bending way that it works. You don't choose to be in heretical mode or not, you are just in it whenever you are cruising at a road speed higher than (engine rpm/final drive ratio)*tire circumference.

In your list, item 4 shouldn't really be there, but the driving technique in item 4 should be kept, as a rough indication of how one achieves a 'glide'.

 

NONE of those things you have listed will make any "significant" difference in your fuel consumption.....by themselves.

 

Using this will actually cause you to have worse (higher) consumption (higher L/100 km/lower MPG). It is also very hard on the HV battery. Valid use case scenarios for the EV switch are situations like a) starting the car to move a short distance, e. g. moving the car out of or into the garage; b) moving slowly in a parking building/structure where you don't want to be emitting pollution.

This sounds like your 5 below. The correct Pulse and Glide technique is to accelerate to a speed you like, then get the foot off the gas pedal for a second then gently apply pressure very slightly so that there are no energy flow arrows showing at all on the Energy Monitor screen. You will still slow down but at a much slower rate. This technique is really only practical at speeds less than 66 km/h (41 MPH), but is really effective in getting lower consumption (higher MPG).
Energy Monitor screen:

I would hazard a guess that it is: Coast/re-generate mode: accelerate to a speed you like, then get the foot off the gas pedal, the car will slow down, but at a quicker rate than 3 above.

This, in my opinion, will also not help achieve lower L/100 km (higher MPG), either.

If you are interested in low L/100 km, use RON 95 fuel and keep your tyres (tires) inflated to the recommended pressures of 230 kPa (rear) and 240 kPa (front) or 5 kPa higher (at most. After this, there are diminishing returns. While talking about tyres, make sure you use good LRR (low rolling resistance) tyres at your next tyre change, if you are not using LRR tyres now.

 

Number 4 is actually the technique used to get the ICE to charge the tractor battery and maintain speed at the same time. You accelerate to posted speed and then ease off the accelerator until the hybrid display power path shows only the ICE providing power to the wheels while it simultaneously charges the battery. Once you do this, you can even slowly accelerate with this technique as well.

At some point you need to re-charge the tractor battery. This is the most efficient way of doing it. Using this technique, you can charge the tractor battery while still maintaining better than 40 mpg. Combine this will glide and you can get a net fuel efficiency of up to 70 mpg with a gen 4 vehicle.

 

A TRACTOR battery in my Prius ??
Where is that one located ??

 

Tricky. Yes, it is possible to drive in such a way that you are regenerating exactly as much power as the car needs to stay in "ready" mode, operate the HVAC, power steering, etc. On a level road this would involve a deceleration. If you descend a hill of exactly the right grade, you could maintain a constant speed.

However, there really isn't any instrumentation with enough fine detail to guide you in balancing on that edge. You could theoretically add that with a scangauge or smartphone app pulling data from the ECU.

 

No. Heretical just doesn't belong on your list.

All the other items on your list are ways you can drive, which you were trying to compare, in the interest of driving for best mileage.

"Heretical mode" is an internal detail of how the transmission works, which, if you're not a mechanic or scientist, just doesn't interest you.

 

No, I'm saying you have an automatic transmission, and it will decide when you're in 6th and when you're not, and you don't have any button to make it happen when it isn't, or make it not happen when it is.

If you're in overdrive and you want to accelerate harder, you'll push the pedal down harder, and the car will 'downshift' out of overdrive to make that happen. When you're done doing that, it will go back.

(Of course it's a CVT, so there isn't really a 'shift' involved; if you have a monitor for your engine rpms and you know the final drive ratio and your tire size, you'll know you're out of 'overdrive' when the engine rpms go above road speed ÷ tire circumference ✕ drive ratio, and you're back in 'overdrive' when the rpms go below that. But if you're not a mechanic or a scientist, you probably won't be bothering yourself with all that, and you'll be fine.)

So the idea of 'controlling' heretical mode as some extra thing you could do as a driver isn't a thing, and doesn't belong on your list, which is otherwise things that you as a driver can do.

The only 'control' you have here is to minimize your hard accelerations that would pull you out of overdrive, but you'll be doing that anyway if you want to be efficient, and putting a fancy word like 'heretical' on it won't change how you do that.

For some purposes, like getting up to speed from a stop, you can be arguably more efficient by just giving enough go pedal to reach your desired speed in a reasonable time, compared to accelerating super gently but for a much longer time.

 

^ I think it is possible that Ipf has been considering heretical mode in the context of the report from that hybrid assistant app. I am not directly familiar with this, but I suppose it is worth pointing out that heretical mode is not exclusive of the other modes. It's simply something that happens, generally once you exceed a certain speed.

 

I haven't used the app ... does it do something like tracking and reporting how much time the transmission is operating in that range?

 

Look at the table included in the graphic in post 12. I think that's where the confusion is coming from. Heretical mode is listed as a percentage of time driven. It is not made clear that this is completely independent of other "modes" or identified driving behavior. It's obvious that the total of those percentages can't be 100.

Now, I get it that heretical mode is just what happens once you've crossed a threshold for ground speed, but this is not made clear in the table shown in the image posted above, and I don't have enough (any) familiarity with the app to use as a basis to suggest an improved interpretation to the o.p.

 

Ah, ok, I hadn't spotted that little table in #11 before. Yeah, the app is just inviting misconceptions by presenting it that way.

To speak carefully, hereticalness doesn't simply depend on a threshold for ground speed. It's the relationship of ground speed to engine rpm. If you are cruising gently at a moderate speed, you'll be in heretical mode. At the same road speed if you're accelerating moderately or pulling up a hill, you won't be.

Given that the engine has a max rpm, there will be a certain threshold of ground speed above which you can only be in heretical mode, but that's a highish speed. I don't remember what it is offhand, and I note sadly that E. A. Hart's classic animated Prius nomograph was apparently done in Flash and therefore is no longer sure to run in today's browsers.

In traditional transmissions, the 'normal' range was considered to cover rpm reduction (turning the differential more slowly than the engine but with higher torque), all the way up to 1:1 (engine rpm and torque reaching the differential unchanged). A gear above that (turning the differential faster than the engine but with less torque) was considered 'overdrive'.

When the transmission is continuously variable as it is in a Prius, the distinction is kind of a nothingburger. Nothing changes very much as the in:out ratio climbs up from .9 to .99 to 1 to 1.01 to 1.1. This app will count all the time above 1.0 as 'heretical mode', but meh.

 

Sorry. That should be "Traction Battery".

...and I can't blame it on spell checker either.

 

You've put it much more carefully than I; I admit to sloppiness in my description but I'm convinced we have the same understanding mechanically.

And that nomograph was rad, I fired up an antique browser to enjoy it a few months back.

I guess the point is that the app can have a counter for % of miles where a cute girl noticed the driver saving the environment. That really could happen at any time. But it doesn't happen at the exclusion of any other driving mode or condition, it's just another layer to be considered on top.

Heretical mode does not count against the other "modes" listed in that table.