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

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 -

 

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.

 

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?

 

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

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.

 

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

 

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.

 

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

http://techno-fandom.org/~hobbit/cars/prius-rally-hints.txt

 

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.

 

Someone asked me today if you could save the values stored in memory before disconnecting the battery then put them back after the battery is reconnected. Is that even possible? If it is volatile memory you should be able to write to it so it sounds reasonable.

 

It's only possible if you are given read/write access to the memory. I am not aware of any way to do this, otherwise it should be a common service practice.

If your friend is just replacing a battery, he can maintain 12 Volts on the system while he swaps out the old battery. Connect the maintaining source to the jump points under the hood.

Tom

 

Most ECUs with a knock sensor will remember the advance curve that is optimum for the fuel and the condition of the engine so they don't have the engine knocking all the time.

 

So, ...

... it seems the prius does *not* learn the driver's driving habits and adjust driveability to match them. Any info to the opposite?

 

"Long Term" to an ECU is only maybe every 2-5 seconds. STFT (short term fuel trim) is continuous and once it needs to deviate much more than 3% (plus or minus) from the programmed tables, it is stored as a LTFT correction and the short term reverts to a "new" zero point. LTFT may take several days to populate after a clear has occured (losing battery power or a ECU "reset" done with a scan tool). This is because many "blocks" must be populated. The only way this will happen is if the engine is cruising in every different rpm and MAP values that define the block tables. Normally the only driver specific habits that influence any stored values were related to transmission shift points. A Prius has a CVT so no shift points are necessary. It does however make sense that the Fuel Mileage Calculation could benefit by long term corrections that would get more accurate with a bigger database of information.

 

The only thing that page in that PDF is saying is that a historical data is saved and used to refine the MPG calculation.

The whole learning theory sounds like science fiction. I haven't found anywhere any evidence of this technology being applied in a Prius. Is it possible? From the technical point of view it's possible. For example, Microsoft handwriting recognition feature is capable of learning from your handwriting but if multiple users are using the same profile instead of an improvement in the recognition process you will get exactly the contrary. And that's the scenario that already somebody described here in this thread. In very few occasions our Prius are driven by just one driver so to implement such technology in it we need profiles/accounts and I don't see this anywhere in my Prius or any other Prius yet.

So what? The historical data will be saved again and unless you have a bipolar disorder the end calculations of this new set of data will mimic the previous results stored before the reset. Oh, but don't let anyone else drive your Prius during the "learning period".

Do you know how many times your Prius was taken for a test drive before you bought it? I should have asked to erase the old historical data before I left the dealer.

 

Whether it sounds like science fiction or not, from my personal experience, it would indicate that there is something to this. And if you look at the MS handwriting recognition analogy you used, in reference to multiple drivers, you may well be onto something.

I have twice (on two different Prii) had to disconnect the battery, once on one Prius to replace the 12V battery, and once on the second Prius the 12V went completely flat and so lost all car settings. On both occasions within a few weeks I started to see a marked improvement in fuel efficiency compared to what I was able to do before. On both cars, through circumstances I became the exclusive driver, but not exactly at that point. Prior my wife also shared driving duties.

On one Prius I struggled to achieve better than 38.6 - 41.3 MPG (6.1 - 5.7 l/100km; 46.3 - 54.3 MPIG) and then after was able to see 44.3 - 54.7 MPG (5.3 - 4.3 l/100km; 53.2 - 65.7 MPIG). I don't know what specifically to attribute the improvement to, as the reset coincided with installing a new battery, and, I had recently changed the front tyres to not specifically LLR tyres, but lower RR than before - Yokohama C.Drive 2. I know I deliberately did not change my driving style, (and I know my wife did not either!), as I was keen to see if the new battery and tyres made any difference. Furthermore, I did continue to see continual improvement in FE, taking into account seasonal variation. Because of these various changes, I always wondered what exactly made the difference battery or tyres, or both.

On the second Prius, the only thing that changed was the 12V being disconnected. I saw similar improvements after about 2-3 weeks. Since then I have changed the rear tyres to Goodyear Assurance Triple Max (from GY Assurance) and have seen a small improvement there too. My Consumption was around 45.2 - 47.0 MPG (5.2 - 5.0 l/100km; 54.3 - 56.5 MPIG) and now it is in the range of 52.3 - 56.0 MPG (4.5 - 4.2 l/100km; 62.8 - 67.3 MPIG). I'd like to point out that initially my wife drove this vehicle, but since I have driven it exclusively (in the last 3 or 4 tanks) I have been able to continually improve FE. This is in part to our different driving styles and I do focus on improving FE more than her, so that is definitely part of it, but, I have not done anything particularly different and the last 2 tanks and still have seen an improvement in FE.

I will be interested to observe what happens when my wife can again share driving duties.

You sound incredulous, but I do not think it is so far fetched. Yes the historical data will be save again. You may or may not mimic the previous results. If you are focused on continual improvement (and not necessarily be bipolar), presumably the data stored will be different. I would especially be leaning toward your last statement, even though you meant it in a sarcastic way.

You may well be being facetious, but I have had those exact same thoughts, and after my experiences, would say you should do exactly that. If you do not have any prior hybrid driving experience and have learned to use any particular hybrid driving techniques, I'd go as far as to say wait year or more then reset the ECU. In saying that, am I seeing that the car is continually monitoring and updating to adapt to new conditions?

Has anybody else made similar observations?

 

You are trying to start an argument about a post from almost 6 years ago? You need to find a better hobby.