I would like to understand the decision criteria that the IMA uses to decide whether or not to engage the auto-stop feature of the HCHII.

Our HCHII seems to be very intermittent on the engagement of auto-stop, and seems to be doing it less and less lately.

For every 20 times I stop in traffic, the auto-stop will engage only once or twice.

Can anyone describe what determines when it engages?

From my experience, the engine temperature needs to reach a certain level before auto stop will engage. Battery temperature also seems to plays a role because if it's fairly warm outside, I sometimes only need to drive a block or two, and autostop will engage (and that's with only a 30 second or so warmup).

Also, if you tend to fluctuate the amount of pressure that you apply to the brake pedal when coming to a stop, there is less chance that autostop will engage (or more accurately, it will engage momentarly and then disengage if pressure on the brake pedal is decreased).

I'm basing the above thoughts on my personal experience and some assumptions. I don't actully know the criteria that the IMA computer uses.

I have noticed 3 factors:
1. The car must be a certain temp. -it heats up faster on hot days, or if you have driven the car w/in the last 30 min or so
2. The defroster must be OFF
3. If you are on a hill and are not pressing firmly on the brake pedal, you begin to slowly roll back as the engine shuts off. As a safety feature, the engine starts back up to keep you from rolling back.

Hope this helps

Having the air cond. on can also effect auto stop, I beleive? Once my car warms up it auto stops 100%. I use the Auto setting on the climate control set at 27 c or 78 f. You could try this, it may solve your problem? Worth a try anyway. H

My girlfriend must fluctuate the pressure she applies to the brake pedal, because a number of times the auto stop didn't engage when she came to a red light. She's learning, though! I'm probably a pain in the *** to drive with, because I'll shout things out like, "Don't creep!"

Gary;

This behavior is by design and has been discussed at lenght since the HCH-II was introduced.

Basically, you get two "free" auto stops unless your speed reaches or exceeds 7MPHG (12Km/h) after the first stop. So, if you are in bumper to bumper traffic and your "move forward" never reaches 7MPH, then auto stop will not resume and the gas engine will remain on. This condition will reset itself to the two free auto-stops as soon as you meet/exceed 7 miles per hour.

Also, this behavior is only likely if :
-The gas engine and emissions system is properly warmed up
-The battery SoC is at a nominal range.
-The usual high drain devices are inactive (defroster, belt driven AC scroll compressor, etc)
-The temps outside are within nominal ranges
-The IPU/MCM/DC-DC/BCM temps are within normal specifications


Many people ask: Why does it behave like this?
The common answer is that starting the engine is a high drain operation on the small NiMH pack and obviously if the vehicle does not achieve a reasonable speed it is likely that the frequency of needed auto-stops would increase with little chance to be balanced by regen opportunities. We have to remember that the climate control, lights, accessories, braking and the power steering are fully active and available while in auto-stop and those can eat the pack charge quite easily on their own.


Cheers;


MSantos

This is our warm weather time of the year, and the AC is on most of the time, but even with the compressor off, the auto-stop rarely comes on. I notice that when I come to a stop, the RPMs drop below 500 then they pop back up to 900 or so. It is almost like the car wants to go into a auto-stop mode, but at the last moment it changes its mind.

Humm... there clearly is a condition that forces the auto-stop to be cancelled.

Couple more questions just 2 B sure:

-How do you operate the climate control (do you use it in auto or do you set it explicitly)? If Auto then what is your strategy for setting the temp?
-And how do you ensure that the compressor is off? Do you turn see "AC off" text on the display?

Anyhow, if the auto-stop is canceled that often (19 times out of 20), then something is wrong. The list of inhibiting conditions I listed in my previous post pretty much provide a good set of starting points when looking for clues.

I would also add that the brake pedal actuator unit may also need to be looked at (at least just for giggles).

What I am trying to say is that a visit to you local dealer may be in order here if you still cannot identify the reason for your canceled auto-stops.

Cheers;

MSantos

-How do you operate the climate control (do you use it in auto or do you set it explicitly)? If Auto then what is your strategy for setting the temp?

Usually it is set at auto with the temp set at 77 or above.

-And how do you ensure that the compressor is off? Do you turn see "AC off" text on the display?

Yes

One other thing is that currently I am also having problems with the electric steering rack. It makes clunking and popping noises as it goes from lock to lock. We have a replacement on order, so after it is installed, I will revisit this problem. I am hoping that they are related.

Indeed.

The power steering is electric and if it is malfunctioning with possible high drain symptoms it could (conceivably) reduce your chances of a frequent auto-stop routine.

What's your state of charge base-lining at? Do you find it getting as low as 4 bars often & quickly?

If so, this could be a solid indicator... and I would be remotely hopeful that the steering rack replacement would restore the car to its normal baseline.

Cheers;

MSantos