Seemingly counter productive actions in cruise control

A couple of weeks ago I put in a new OEM battery and this last week drove from LA to the bay area and back. Almost all of that was using the cruise control, typically set at 72 mph. Never observed the SOC fall below blue at any point during this trip.

Some strange things happen doing that, especially on hills.

On downhill slops the car would frequently be pulling current from the pack, rather than charging it up. Not just when the SOC was in the green, also when it was in the blue. The majority of the time it would be charging though.

On climbs the car would frequently be pushing current into the pack. Again, in both green and blue SOCs.

For some reason or other after climbing the grapevine (a very steep 8 miles of highway) the pack was never out of the blue, I think it went down to 4 bars at one point, but it took many, many, many miles of downhill travel before it went into the green. In fact I don't think it did until I had to briefly shift into B mode for extra braking. Which is really peculiar because at lower speeds, driving in town down much shorter and less steep grades it will get to green easily.

The instantaneous MPG displays are all over the place on long straight (but maybe tilted up or down) road. That is, the road in question is like a ruler which can be flat or tilted, but doesn't oscillate up or down noticeably. It is almost like the cruise control is constantly hunting for a setting and goes too far in one direction, then the other, without ever converging on, and sticking with, the optimum setting. For instance, on flat road I have seen it wander around between the mid 30's and 99 where the mean would be something like 47 or 48. No cars nearby, no wind evident in the vegetation near the road, didn't touch the brakes, gas, or cruise control adjustment the whole time.

Maybe it is too much to ask for, but when presented with a long period of driving along under exactly the same conditions, shouldn't a cruise control eventually settle on the right amount of fuel to just sit stably at the set speed?

 

There was no wind at all for most of the trip. Not only was there no motion in the vegetation, but at the stops it was calm too. I cannot rule out something so gentle it was essentially imperceptible, like say a 1/4 mph breeze.

It wouldn't be that hard to set up a cruise control which could detect when the current optimum throttle position no longer was. If it saw the velocity increasing or decreasing by a couple of mph for the same throttle position then it would know it needed to change.

I wonder if part of this hopping around is related to the incessant charging and discharging of the pack. At lower speeds, like 40 mph, and especially going down a slight grade, it is possible to turn off the motor and the pack (energy display paths all black) with a slight bit of throttle pressure. Going a steady 72 mph on the flat though it seems like the cruise control has no way to take the pack out of the equation, and certainly it can't turn off the motor. But in theory at a perfectly steady speed on the flat it doesn't need, or even want, the pack to be moving current. So it ends up slightly overcharging the pack, sees that isn't right, turns off (or down) the motor (resulting in the high MPG reading), then finds it is undercharging, cranks the motor back up (resulting in the mid 30's mpg) and just bounces around like that.

I don't have a conventional ICE car with cruise control that also shows instantaneous MPG. Do they settle to (near) constant MPG under static conditions or do they bounce around too?