Toyota Prius Forum banner

1 - 17 of 17 Posts

·
Registered
Joined
·
1,002 Posts
Discussion Starter #1
I had an odd experience a few days ago. I was stopped at a red light, and the ICE came on for no apparent reason. I had just gone down a long hill, so I knew the battery shouldn't be low. It was about 70 F outside, so both heat and A/C were off (I had it on fan only, lowest setting, low enough temp that the heat shouldn't have been on,) as were all other electric accessories. I switched to the 'energy' screen to confirm, and it showed a full 8 bars on the battery, and showed battery and ICE power going to the wheels, even though I was at a complete stop. I shifted to Neutral, and the ICE immediately shut off. The traffic signal changed just then, so I wasn't able to experiment further.

Any ideas?

Oddly, this happened at the end of the highest-mileage reasonably long drive I've had so far (26 miles of flat driving at 60-70 mpg on a 40-50 mph country road, maybe 1/3 with the windows down.) It was 13 miles one way that started with a large up hill to reach the flat road, stopped for about 10 minutes, then the 13 miles flat back to go down the large hill again.
 

·
Registered
Joined
·
165 Posts
Yes, ICE can be used to drain the battery in some cases, as you proposed.

As you probably know, the Prius HV battery is extremely well protected against deep discharge and overcharging, since both would reduce battery "life". If you drive down a mountain pass, for instance, it can happen that the battery is "full" before you reach the bottom of the valley. Actually "full" is not the right term, since it's somewhere near 80% state of charge, but it appears as full on the multi-display. What happens then, if there's still some downhill driving left ? The engine kicks in, but without fuel injection ! In other words, excess electricity is used to spin the engine, which acts as a brake, since there is no gas in the cylinders. And if you were already in "B" mode before it happened, then the engine would simply spin faster...

As I am living in a mountain area, I experienced this several times, but most drivers won't. In your case, the oddity was that it happened as you just stopped. And since putting the car in "N" cancels all energy management (therefore the warning message if you open the door in "N"), it's normal that the engine stopped in this case too. Now, the meaning of the arrows on the screen in this very special case could be a little confusing and not representative of what happens really, since the sketch is oversimplified (1 motor instead of 2) and the case "arrow flowing from the generator to the engine" has probably not been considered by software engineers... :wink:
 

·
Registered
Joined
·
1,002 Posts
Discussion Starter #4
frenchie said:
What happens then, if there's still some downhill driving left ? The engine kicks in, but without fuel injection ! In other words, excess electricity is used to spin the engine, which acts as a brake, since there is no gas in the cylinders. And if you were already in "B" mode before it happened, then the engine would simply spin faster...
This wasn't the normal "Braking mode" engine spin, this was an actual gasoline-burning event. Just like after you first turn it on, or when the battery gets too low. The ICE had *NOT* been running down the hill (it wasn't so long as to make it go into B mode on its own, which I have experienced before,) it only came on after I had already come to a complete stop. It *SOUNDED* like a gasoline-burning engine run, although I suppose I can't be certain of that.

The hill wasn't so long that I can imagine it cooling the engine off. Again, it was a reasonably warm day. The hill in this case wasn't even that long, it was just that I had been down a long hill only minutes earlier. There is a combination of two hills that I go down on a fairly regular basis where the first hill gets it to 7 bars of charge, then I usually use up 1 bar on level/slight-up, then down the second hill that brings it to 8 bars. This was that second down hill segment. This had never happened before.
 

·
Registered
Joined
·
16 Posts
Sorry, I do not think Toyota would design such a fuel efficient car and then waste away the energy this way. There must be some other good reasons why ICE must be on, eg. for emission control.

I've been searching the USPTO site and I believe the following patents may help to explain what you 've observed:

http://www.uspto.gov/patft/index.html

Patent# 6,032,753 from Toyota
On the hybrid vehicle, the engine can be driven by the power smaller than the required energy for running, and a fuel cut control that temporarily cuts a supply of fuel to the engine may be carried out frequently and for a long time period. The temperature of the catalyst is often lowered to an undesirably low level in such cases.

The object of the present invention is thus to provide a catalyst temperature control apparatus for a hybrid vehicle, which warms up a catalyst quickly and efficiently and maintains a high conversion efficiency of gaseous exhausts even in a specific driving state of an engine, in which a catalyst is cooled down by relatively low-temperature gaseous exhausts.
Patent# 6,427,793 from Honda
In such a parallel hybrid vehicle, when motor travel continues for a long period of time, as the engine is stopped during this period, no high temperature exhaust gases which are expelled by the engine while the engine is driven flow in the exhaust passage during this long period of time, and as a result the temperature of the catalyst in this exhaust passage drops, and this negatively affects the ability of the catalyst to clean the gases.

In such situation, there is a problem in that if a travel mode of the hybrid vehicle is switched between engine travel and motor travel at a later time, then whenever switches to engine travel are made, the exhaust of harmful materials is increased at once after every switch.
Patent# 6,397,963 from Ford
The method includes sensing that an engine of a hybrid electric vehicle has stopped operating. A time period is predicted after which a catalyst of an emissions system associated with the engine will cool to a light-off temperature below which the catalyst becomes ineffective. The predicting step is based on known qualities of the catalyst and ambient conditions in which the vehicle is being operated. The engine is restarted when the predicted time period has expired thereby maintaining the catalyst at temperatures in excess of the light-off temperature.
If I were you, I would just let the ECUs decide for itself and not shift to 'N'. The ECUs are monitoring a lot of sensors and switches so are in a better position to decide what is best.

Just drive it as what others have said before. :!:

Vincent
 

·
Registered
Joined
·
1,002 Posts
Discussion Starter #6
vincent1449p said:
If I were you, I would just let the ECUs decide for itself and not shift to 'N'. The ECUs are monitoring a lot of sensors and switches so are in a better position to decide what is best.

Just drive it as what others have said before. :!:

Vincent
hehe.. Yeah, normally when it comes on, I just let it stay on. In this case, the circumstances were odd, so I thought something may have been wrong, so I shifted into 'N' to see what would happen.
 

·
Registered
Joined
·
1,215 Posts
I agree with Vincent in principle.

It doesn't happen very often, but when it does, it really irks me when my hybrid decides to run the ICE at ANY red light or stop sign, or at anytime that I am driving under 8 MPH, particularly when the MFD shows plenty of battery juice remaining to maintain lights, AC, etcetera (ie - anything in the blue or green ranges (3 to 8 bars)).

I can understand the ICE coming on when I'm "in the red" or when I have the AC on "max." But if I'm not driving, and it's not in the red, then let's work together on this, wait a minute and burn the gas when I start moving again, okay?
 

·
Registered
Joined
·
181 Posts
If the ICE came on, it probably did so to charge the battery or some other function. you said you had just come off a fairly long hill. well, just came off would mean you were sitting at a light at the bottom of the hill you mentioned. if you werent, then it is very possible the battery simply needed a boost.

realize from a full SOC to very little charge (in the displayed SOC range of course) equates to only a few miles of range. many have reported only being able to go a mile or two after running out of gas.

so dont think that the battery will take you far because it wont. dont think that that big hill will take care of all your needs for the next 10 minutes, or even 2 minutes, because it may not.
 

·
Registered
Joined
·
130 Posts
Maybe if you just treated the MFD as a "toy" Would you believe it, the car runs just as well when MFD is turned off. You would really be amazed at how often the "ICE" runs without any indication on the MFD
 

·
Registered
Joined
·
165 Posts
I agree with Vincent, besides battery life clean emissions is another strong reason for the Prius to run the ICE, paradoxically... that's also why Prius-type hybrids will never have large capacity batteries even if they become light and cheap : you must run the engine often anyway in order to keep the catalyst warm. Or someday we'll see electrically heated catalysts, maybe ? :wink:
 

·
Registered
Joined
·
1,002 Posts
Discussion Starter #11
Mass Reply...

Olympic Dave: Yes, it was at the bottom of the hill. As in, if I had released the brake pedal, the car would have started rolling forward into the intersection. The battery was 'full' on the screen.

zinzin: I do realize that the ICE does run often, I usually keep the MFD on 'Consumption' (the half-hour bar graph,) instead of 'Energy' (the pretty blinkenlights screen,) specifically because I don't want to get overly distracted. I have noticed the ICE come on many times in the past at times that didn't seem appropriate (such as with a full battery while accelerating from a stop light slowly enough that I know I'd used just battery power before when the battery was less full.) My point is that in this case, it seemed VERY VERY odd that the ICE was coming on.

frenchie: Yes, I know that the catalytic converter must be kept hot to maintain good emissions. It wasn't so long of a hill that that seemed to be a valid reason, though. Just two days ago, I drove down a mountain (Mt. St. Helens in Washington state,) and was going downhill for over half an hour, with the ICE only coming on only once (with gas.) I could hear the ICE spinning to absorb the extra energy after the battery was 'full', so just to check, I hit the gas pedal hard enough to use ICE power, and I could tell when it was 'just spinning' from when it was using gas. That was the only time in half an hour that the ICE used gas. (Therefore, the only time it was generating emissions to warm the catalytic converter.) The outside air temperature at the time was 56° F. Oh, now that I think about it, we were parked at the top with the car 'on', eating sandwiches and listening to the radio for half an hour before starting down the mountain, so the ICE was off (yet the Prius was in 'on' mode,) for almost an hour, yet it never seemed compelled to start the ICE to warm the catalytic converter during that time. (Unfortunately, I did not think about coming to a complete stop at the bottom of the long downhill drive to test my 'power drain' theory, I just got right on the highway, where the ICE did come on to get me up to (and maintain) 70 mph.)

The time I am talking about where the ICE came on without apparent reason, it was about 75° F out, and I was at the end of a half-hour city drive, with the ICE regularly on. The hill in question only took about 5 minutes to go down, so I doubt the catalytic converter would have cooled off too much in that time.

It just seemed like a VERY VERY odd that the ICE came on at that moment, that's why I questioned it enough to post here. The other odd one was that the display showed that the ICE was applying power to the wheels, when it decidedly was not, since the car was at a complete stop. I would not have even gone to the 'Energy' screen had I not been certain that the battery was sufficiently charged to not need ICE charging.
 

·
Registered
Joined
·
181 Posts
its just normal operation. mine does it too and there is no rhyme or reason to it really. the ICE obviously has other duties to take care of besides the charging of the battery and motion of the car.

one thing to note, if the car is in park and "idling" it will go HOURS without the ICE starting. several times i have had a full screen of 0.0 mpg from sitting and the car never starts up once.

so part of it i think has to do with whether or not the car has been moved lately and what gear its in.

i do know that its weird when a car that is not supposed to idle at stoplights will all of a sudden start running before the light turns green. i thought that strange too, but as i said, its normal. when my mileage drops below 50 mpg, then ill start questioning it.
 

·
Registered
Joined
·
1,434 Posts
I've been ignoring this thread b/c I though I'd already answered the question...turns out I don't see my name anywhere in the thread.

The reason the ICE came on with the full battery was to drain some of the charge. You already know that the ECU prefers to keep the SOC of the battery in the blue range...it doesn't like green any more than it likes pink. If you're actively driving the car will preferentially use the battery power. If you're stopped it will cycle the ICE on then off several times. MG1 puts a pretty good drain on the traction battery to accomplish that so it is pretty effective at draining the battery to a more satisfactory (to the ECU) level.
 

·
Registered
Joined
·
515 Posts
Evan is quite correct. He also got me thinking about thread responses...

It simply wouldn't be fair to the newbies to deny them the discovery process opportunity. Allowing a "new" topic to run its course can be quite rewarding for the participants. So I intentionally hold off on certain posts sometimes, not jumping in unless a totally incorrect conclusion is drawn.

That actually makes it rather exciting for me too. There's more well informed people out there now. Yeah! It was quite lonely at first. Now the number of gurus is growing. Sweet! Eventually, the same questions won't re-emerge as "new" topics anymore.

I wonder when that will be? There's lots of misunderstandings & misconceptions out there still.

By the way, now that it's getting cold, watch for the "why does the engine surge" topic. Someone will end up posting it again. The answer to that question is the emissions system is simply taking advantage of an opportunity to burn off certain collected pollutants.
 

·
Registered
Joined
·
381 Posts
john1701a said:
By the way, now that it's getting cold, watch for the "why does the engine surge" topic. Someone will end up posting it again. The answer to that question is the emissions system is simply taking advantage of an opportunity to burn off certain collected pollutants.
Thanks for the "reminder"; I got my 2004 after the "cold" (?) season down here was over, so I never experienced that first-hand; will keep a... something... open for it. :)
 

·
Registered
Joined
·
16 Posts
I know this topic is not "new" as I 've also read it many times in other forums.

I think the earliest I saw was in YG where Wayne Brown posted his replies on this battery draining observation. Someone pls correct me if I'm wrong. Or if anyone has other sources of infomation, pls post it here. Thanks!

As there are no opposing views to his, I 've also believed him as he is always correct. Although sometimes he realise his mistakes when someone sent him msg. through private mail, he quickly admitted it and posted his corrections immediately. This has made me respect him more.

It is only recently that I started to read the patents and there are explanations that do not agree to what I 've believed. This has bothered me for sometime and I actually wanted to post my questions to him but he is not active in YG anymore. That is why I chose to post it here and hoping that some other gurus would shed some light on this.

Here are more questions:

1. If the car knows that it has to drain off some charge when it reached 80% SOC, why not cut-off regen. at say, 75% or lower. Using the ICE to drain later not only waste energy, it also produces more pollution.

2. What happens when you "forced charge" the battery by depressing the brake and accelerator at the same time? According to the battery draining theory, the charge should drop immediately after you release the accelerator when it reached 80%, right?

3. Can the miniscanner read catalyst temperature? We know the catalyst begins to operate at around 550'F and efficient purification does not take place until it reaches at least 750'F. If we can observe the threshold temperature, then we will be able to verify whether the patents are right or wrong.

4. Why not use electrical means to heat the catalyst as what frenchie has mentioned? If I remembered correctly, there are some patents on this as well. The problem is that it takes longer time to heat it this way than using hot gas. Besides, the SOC of battery may sometimes gets too low for this purpose.

Appreciate any comments. I 'm learning everyday.

Vincent
 

·
Registered
Joined
·
7,166 Posts
The absorbtive catalytic was for the classics. The 04-05 have the traditional catalytic.

It may not be a good idea to achieve proper catalytic temp, but perhaps it could be used to maintain it? Of course that would depend on ambient outdoor temp.
 
1 - 17 of 17 Posts
Top