How/What Does the Prius' CPU(s) "Learn?"

[Rokeby]

In a number of threads it has been reported that as you drive your Prius it
"learns" something over time. Also, if for whatever reason the 12v battery
is disconnected, the CPU(s) memory is at least diminished, if not outright
erased. Afterwards the CPU(s) has to "relearn" what it formerly knew. This
it has been said is evidenced by the FE/MPG dropping for a short period, up
to a few tanks of gas.

I'm getting decent FE, +/- 50 MPG and rising, no complaints. The CPU(s) and
I seem to be learning well.

First question; Just what is it that the CPU(s) "learn?" Is it about my style of
driving, something like, "Goes easy on the blue bars, don't have to keep the
HV battery at a high six bars." If you've got GPS, is it the terrain and your
typical routes? (This would be very interesting and perhaps even downright
scary.)

Perhaps households with two Prius can help here. If the two drivers have
vastly different driving styles, does each get noticeably different FE/MPG
when you drive the "other car." (Yes I know, a highly unlikely event.)

Second question: Does the car act or seem obviously different? Like maybe
it's a little confused or hesitant in some way?
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Summary and consolidation of postings through April 12, '08 appear in
Posting #17.

[kocho]

I highly doubt the CPU learns my driving habits. Could "Learning" be a misconseption based in the fact that the CPU needs to go thru several driving cycles and specific driving conditions to complete all sensor and checks inspection cycles.

But someone might surprise me with a fact how learning happens - the above is just my guess.

I see not difference in driving dynamics before and after a DTC reset. Not sure if this counts as a CPU recet...

I know that certain components do adjust to driving style, but that is based on immediate data while driving. All is forgotten moments later, when conditions change. For instance, a transmission might shift more aggressively if you floor the gas pedal. In my Camry, the A/C cuts off at full acceleration to add a few HP to the wheels where it is presumably needed. VSC also reacts to your driving as does speed-sensitive steering. Not sure if anything else does, besides a "memory" driver seat or steering wheel -

Originally Posted by Rokeby

In a number of threads it has been reported that as you drive your Prius it
"learns" something over time. Also, if for whatever reason the 12v battery
is disconnected, the CPU(s) memory is at least diminished, if not outright
erased. Afterwards the CPU(s) has to "relearn" what it formerly knew. This
it has been said is evidenced by the FE/MPG dropping for a short period, up
to a few tanks of gas.

I'm getting decent FE, +/- 50 MPG and rising, no complaints. The CPU(s) and
I seem to be learning well.

First question; Just what is it that the CPU(s) "learn?" Is it about my style of
driving, something like, "Goes easy on the blue bars, don't have to keep the
HV battery at a high six bars." If you've got GPS, is it the terrain and your
typical routes? (This would be very interesting and perhaps even downright
scary.)

Perhaps households with two Prius can help here. If the two drivers have
vastly different driving styles, does each get noticeably different FE/MPG
when you drive the "other car." (Yes I know, a highly unlikely event.)

Second question: Does the car act or seem obviously different? Like maybe
it's a little confused or hesitant in some way?

[dogfriend]

I have experienced this phenomenon when I disconnected the 12V power so I could remove the seat without worrying about the Side Airbag going off. It took a couple of tankfuls before the car went back to "normal"

If you lose backup power for the Engine ECU, then I would believe that you would lose the Short Term and Long Term Fuel Trim adjustments. This is data that all OBD 2 systems store to adjust for differences in individual engines.

Also, there is a section in the Tech Training manual that says that the HV ECU stores "Historical Data" to refine the calculations used for the Energy Screen. I am attaching a screen shot of the page.

[Rokeby]

dogfriend,

thank you for the Toyota Tech Manual cite. It is so relevant to this
discussion that I am briniging it directly into the thread:

--------------------------------------------------------------

"Energy Monitor

"The Energy Monitor, which includes a historical bar graph and total trip
economy (MPG), is very accurate. Multiple, comparative calculations are
performed by several computers.

"Fuel useage and fuel economy are calculated by monitoring fuel injector
duration and operating frequency. The ECU compares these values with
miles traveled to calculate miles per gallon.

"The battery ECU closely monitors energy consumption in Watts. By
calculating the amount of energy spent, recovered and stored, the
computer can calculate the required fuel burn. Fuel required to create
this amount of energy is compared against the engine ECU fuel injection
calculation to ensure accuracy.

"Driving pattern, speed, and load characteristics are stored in the HV ECU
as 'Historical Data.' Historical Data is used to further refine the MPG
calculation. This data takes about three to six weeks to accumulate if the
battery is disconnnected or the HV ECU is replaced."

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The last paragraph would seem to explain the oft reported effect of 12V
battery removal on reported MPG.

Of significance to this thread is the question; Just what does Toyota
mean by "driving pattern" and "load characteristics?"

dogfriend, can you find out when the Tech Training Manual was written
and/or updated?

I have a suspicion that it was some while ago, say about 2005.

[Jack66]

I've had the same question, but from the tech manual it seems to imply that the only use of the "learned" data is to make the MFD energy/MPG numbers more accurate?

[dogfriend]

Originally Posted by Rokeby

dogfriend, can you find out when the Tech Training Manual was written
and/or updated?

I have a suspicion that it was some while ago, say about 2005.

No, I don't know exactly when the tech training manual(s) were written, but they cover both the NHW11 and NHW20, so it must be 2004 or newer. You can download it here:

AUTOMOTIVE TECHNICAL ARTICLES

Originally Posted by Jack66

I've had the same question, but from the tech manual it seems to imply that the only use of the "learned" data is to make the MFD energy/MPG numbers more accurate?

My impression from disconnecting the 12V battery two different times (once to study the construction of the seat, and once to actually modify it) is that the mileage dropped as reported on the MF display and miles driven per fillup. I have data of all fillups, but I need to reconstruct my spreadsheet after the file was lost, so I can't give exact figures at this time.

Of course, YMMV.

[qbee42]

Most if not all new electronic control systems on automobiles collect some information that is used for control system tuning. Learning is a reasonable description of the process. Much of the information compensates for minor differences from engine to engine. Yours may have more carbon on the plugs, or perhaps run in a colder climate. Some of the systems also adjust for driving styles.

At present, the Prius has no knowledge of terrain. Work is being done by some researchers to use GPS and topographic data for optimizing the use of the battery, but as far as I know this has not been done on any production vehicle.

Tom

[Jack66]

Originally Posted by dogfriend

My impression from disconnecting the 12V battery two different times (once to study the construction of the seat, and once to actually modify it) is that the mileage dropped as reported on the MF display and miles driven per fillup. I have data of all fillups, but I need to reconstruct my spreadsheet after the file was lost, so I can't give exact figures at this time.

Of course, YMMV.

Thanks, Dogfriend. I still wonder if your actual mileage and FE are effected by the CPU memory loss or if the data displayed on the MFD is not as accurate because it doesn't remember how to adjust the numbers to make them more accurate. I'm sure that the CPU makes some adjustments based on current engine sensor readings but the tech manual gives the impression that the history is used to make the numbers displayed in the MFD more accurate.

[dogfriend]

Hobbit also has a paragraph on this in his page on rally hints:

http://techno-fandom.org/~hobbit/car...ally-hints.txt

Do not disconnect your 12V battery any time within 2 weeks or so before the event. The car's computers learn certain values as you drive, and use them to create best-economy running conditions. If the battery gets disconnected, those learned parameters get erased and fall back to internal defaults which may not be as optimized for mileage performance.

[racerbob]

Long term fuel trim is a set of "cells" in the engine ECU that store adjusted values of fuel mixture control. These are adjusted according to engine characteristics such as age, pumping ability (ring & valve condition, vacuum leaks, air filter restriction), cam wear, etc. When 12v battery is disconnected these may take a couple of days to fill up all the cells (blocks) with useful info. This is a trick that can work to your advantage sometimes in non hybrids when running for 1/4 mile times as the leaner, learned values are erased and replaced with default (usually richer) fuel values.

see: Block Learn Multiplier and Integrator
for a more in-depth explanation.