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Hi all--

So, the new HCHII has been teaching me how to drive all over again. Between Tarabell's article and the FCDs my first tank has climbed from 37 to 42 so far. That brings me to my question:

On my morning commute on cold days I am often unable to reach the right conditions for Auto-Stop to occur, at least not until I'm almost to work. The car is warmed up by that time and I've yet to dip below four bars of SOC, so I'm wondering what else I can do. My commute isn't too long (7.5 miles, about 15 minutes), so getting stuck at a light will send a decent segment south in a hurry.

I know from the owner's manual that the conditions for AS to occur are that the engine is warm, the battery is charged and that the fan can't be cranking. Do I remember reading somewhere else that the pack needs to be at a certain temperature, too?

Well, anyway, any AS advice would be welcome. --RN

Hi HCHCIN:

___One word, “FAS”.

___Good Luck

___Wayne

My car used to do this too on some cold and rainy nights. (and by cold I mean 40-50s in Los Angeles??) It's getting better though - I think what I figured out was to take the fan off of AUTO and switch it to AC off and make sure it's on one level of fan. Although it could have started auto-stopping again earlier for different reasons.

Although I assume you have the heat going too.

Won't FASing (forced auto stopping - you guys are abbreviation crazy!) cause some problems in the long run? What are the long term affects of stopping and turning on the engine all of the time. Won't that wear it down?

-Chris

No one has noticed any problems other than maybe the 12v needing to be replaced sooner, but that all depends on how often you FAS. Most of us don't notice any problems even after 50K miles in my case, and many more miles in other cases.

It will add to wear of certian components, but most if not all cars tend to be able to handle the extra wear.

On the original topic, this recent shift from 40-50F highs to 65F+ has made for some dramatic improvements in the behavior of the Prius. The most noticeable to me is the increased battery capacity afforded by warmer temperatures. It used to be that I would get very little EV time before the ICE wanted to re-light, now it will go for quite a while when loads are low. Indicated SoC depletion is minimal and the benefit is really showing up in my numbers this week.

My commute isn't too long (7.5 miles, about 15 minutes), so getting stuck at a light will send a decent segment south in a hurry.


too bad you don't have a scangauge, i'm curious to see at what coolant temp autostop will kick in, for my car its 40 degrees C or higher. Have you considered blocking off your grille? It might induce autostop earlier and since your commute is very short i see no problems of overheating unless summer is here.

block heater is a good investment too, cold trips is so much worse for the engine than WOT it every now and then.

Hi all--

I guess I never followed up on this, but I think one of the problems that I discovered might be contributing to not getting Auto Stop is that the HCH-II seems to use the air conditioning compressor all the time in "auto" mode, even when what you want is heat (not cooling). So I'm thinking that using climate control, combined with low temps last winter, meant I was prolonging the conditions under which AS occurs. Am I wrong here?

Either way, I'm proud to note that now it's warm my commute is easily in the 55-65 mpg range. Sweet. --RN

Nope, I don't think you are wrong at all.

I regard the operation of the climate control in Auto as a good compromize for most folks particularly when the climate is moderately warm. It also works pretty well in the warmer summer days (90F - 110F) with a little strategic management thrown in. The key is prevent the Auto climate control from working too hard at achieving the desired temperature. If the differential is too high then your FE will get hit hard.

In moderate weather, I always keep it in Auto but I manage the target temps gradually so that the load on the engine is minimal.

On the HCH-2, the Auto stop depends on several temperature variables. Here are some I know of:
- OAT (outside air temperature)
- IAT (Intake air temperature)
- ECT (Engine coolant temperature)
- IPU (Battery & BCM temperature)

Now, as you see I've listed at least four temperature parameters that the 4th gen IMA looks for (there are an additional few minor ones too). In a way they are all somewhat related. One interesting remark is that keeping the passenger cabin at a good temperature is key to enabling the Auto Stop more frequently as well. Too hot or too cold and it just says no.

Cheers;

MSantos

Msantos, could you clarify: "One interesting remark is that keeping the passenger cabin at a good temperature is key to enabling the Auto Stop more frequently as well. Too hot or too cold and it just says no."

I try not to run the A/C at all. Not quite to the ice vest stage, but try to park in the shade to try to keep the car cool. If the A/C is off (climate control display reads "A/C Off"), how would a hot cabin temp keep AS from kicking in? I have not seen this.

Maybe I'm misunderstanding the post. Thanks in advance.

MSantos--

In the winter, if I turn on "Auto" but press the AC button (thereby turning off the AC compressor), will it have an effect on AutoStop?

In the olden days (before automatic climate control) heat was just outside air passed over the heater core, without the AC coming into play. Frankly with how dry the air is in the winter I don't see much need for the compressor to run (unless I want defrost, of course).

Anyway, I assume by "strategic management" on hot days you mean to set the climate control to a high temperature and as that temperature is reached slowly turn it down to a moderate temperature. Is that your strategy? --RN

Msantos, could you clarify: "One interesting remark is that keeping the passenger cabin at a good temperature is key to enabling the Auto Stop more frequently as well. Too hot or too cold and it just says no."

I try not to run the A/C at all. Not quite to the ice vest stage, but try to park in the shade to try to keep the car cool. If the A/C is off (climate control display reads "A/C Off"), how would a hot cabin temp keep AS from kicking in? I have not seen this.

Maybe I'm misunderstanding the post. Thanks in advance.

Sure. No problem at all.

The IPU sitting in the back seat uses active cooling. Basically a fan that is supposed to draw air from the passenger cabin downstream over the various modules (Battery pack, BCM, DC-DC... etc) and then vent it out through a port in the left side of the trunk.

If the interior temps are too high in the cabin then the IPU will invevitably be under higher thermal stress and may take appropriate corrective action.

If the interior temps are too low then the IPU modules may be under governed operation as well. The faster they warm up the quicker they enter the normal operating specifications. Block heaters have a tremedous indirect impact here in the cooler winter months because it when we benefit so does the IPU and the IMA system will return to normal operation faster.


Cheers;

MSantos

In the winter, if I turn on "Auto" but press the AC button (thereby turning off the AC compressor), will it have an effect on AutoStop?


I do that exactly - in my experience, it has a positive effect on the AS. During the winter, heat is the primary requirement needed to restore normal IMA operation sooner. Unfortunately some of us still lose AS for many weeks in a row. To help I (like many) block the front grill in addition to using the block heater regularly.



In the olden days (before automatic climate control) heat was just outside air passed over the heater core, without the AC coming into play. Frankly with how dry the air is in the winter I don't see much need for the compressor to run (unless I want defrost, of course).


I agree. However, I make sure I operate the AC at least once a week for 10 minutes as well just to make sure the AC system and lines remain properly lubricated. Besides, it is a great defrost method.


Anyway, I assume by "strategic management" on hot days you mean to set the climate control to a high temperature and as that temperature is reached slowly turn it down to a moderate temperature. Is that your strategy? --RN


Precisely. I am however always impressed by those folks who endure the hot days with AC turned OFF. It takes alot of guts and will power just to get awesome FE.

But, from where I stand, I look at the technical attributes of the 4th Gen IMA system and I figured that managed AC operation (in Auto mode) not only provides the occupant good comfort but also very good FE and the environmental conditions for a healthy IPU system. The only other big management key here is the battery SoC.

Those are my 2 cents. ;)

MSantos

Very interesting, msantos. I've driven in high heat -- not much over 100F but close -- and also haven't (yet) seen AS not work. But I hope it never gets hot enough to have that effect as I'd really rather not use the a/c.

Now once I ran a/c with compressor on a really hot day, and noticed not only was there no AS, but there was no assist either. (I think the a/c was dialed to the lowest temp though, not on "auto" so maybe that jinxed it)

... Now once I ran a/c with compressor on a really hot day, and noticed not only was there no AS, but there was no assist either. (I think the a/c was dialed to the lowest temp though, not on "auto" so maybe that jinxed it)

If I recall correctly, it was last summer that most of us got hit by +100F weather and many folks reported the temporary loss of assist among other regular IMA features. I also recall some folks complaining about the uncomfortable if not extreme temps in the back seat as well.

That prompted me to investigate the the matter more closely and after we took apart "our" HCH-2 at the university (not mine of course), I noticed that it does not pay to run the IPU too hot at all. The IPU's health and proper operation appears directly dependent on the comfort of the occupants. If I lived in a warmer latitude I definetly would get some tinting on the windows - I thing it would help alot.

Indeed, quite interesting.

Cheers;

MSantos