Dips in charge / discharge current limits --> ICE on?

We just got our prime a couple weeks ago. On a typical morning I drive my daughter to school (5 miles, downhill the whole way), then return home. I've been trying to make the whole trip without the ICE turning on, but have only managed it once so far.

EV mode on. Speed < 84mph. Defrost off. No cruise control. Usually in "normal" mode, not "eco". Outside temps around 20F. Car is not garaged. Sometimes heat is on (but only if temp gauge reads > 14F). Generally car is fully charged (scheduled departure, lvl 1 charger). I do have pre-conditioning selected, but it doesn't seem to actually work.

The trip starts with ~1mi down a steep-ish dirt road going about 20mph. Some regen is happening here. Stop sign at the bottom of the road. Then turn onto a paved road and going about 55 mph, still downhill but less steep. Car is consuming power at this point (not regenerating). Stop (car turned off) at school for a few minutes, then uphill all the way home.

Typically I notice the engine turning on right as I accelerate away from the stop sign at the bottom of the dirt road. This is on the way to school (downhill). It's possible that the engine turns on a little bit before I get to the bottom of the dirt road, but that I'm not noticing it until I pull away from the stop. Only in the past couple days have I been putting the energy monitor screen up and also I learned about the green car icon being just an outline when the ICE is on.

I can usually make the trip home from school without the ICE coming on.

The one successful trip was actually in the afternoon, so at ~40F instead of 20.

This morning I made sure the car was only ~75% charged, thinking the problem might be too much regen on a full battery. That seemed to work, I made it all the way to school. But, then the ICE kicked in halfway home.

I just got the hybridassistant app yesterday, so I had that running this morning (but I wasn't watching it at all). Looking at the report, I'm seeing dips in the charge and discharge current limits, and it seems like exceeding those may be what kicks on the ICE. Is that true? And can anyone explain what causes these dips?

I'm attaching the CCL/DCL plots from the hybrid assistant report. The plot with the dip in the red line is the downhill trip (ICE did not come on). The plot with the blue line dip is the return home, you can see that the engine is on from ~8:21:45 to 8:24:00 (where the green hybrid battery power is about 0). Let me know if more plots would be helpful.

 

Not sure how many miles it would have said. I had the % indicator showing instead and remember it being about 20% just before the engine kicked on. Was thinking at the time it should be just enough to make it home.

 

Right, I get that. That's why this morning I didn't charge it all the way.

No thanks. That's not my style. I like to know all the details of how things work

 

It is not in EV auto.

Does Eco actually make a difference in terms of the ICE coming on? I thought it was just accelerator pedal responsiveness. I usually drive in "Normal".

 

Not sure, as I had the battery % indicator up instead, which showed ~20% battery left. It should have been enough to make it home, albeit without much to spare.

You can see that the graph shows 28% SOC (state of charge) at the point when the engine kicks on. I'm not sure yet exactly how SOC translates to the battery % shown on the MID, though. I have seen an 81% SOC reading when the car says it is fully charged.

Yeah, I'm hitting about 65mph max. ICE comes on above 84 mph per the manual.

 

I see what you're saying, but I don't think that entirely explains it. I agree SOC is probably > 0% when EV range runs out, but in this case I know there was significant EV range left when the ICE kicked in. I'm fairly certain it was reading around 20% on the MID (4-5 miles). You can see in the graph where the engine turns back off a couple minutes before I get home and it uses up more battery. SOC at the end of the trip was 24%, and I'd bet even then there was still a couple miles of EV range left (though I did not check).

I really think it has to do with the dip in discharge current limit. Anyone understand what factors determine that limit or what might have caused the dip?