Gen 2 Hold Mode -- weaker "grip" than Gen 1?

6756 Views 45 Replies 22 Participants Last post by MikeyCVolt, Mar 30, 2018

VoltenRock

Discussion Starter · Oct 8, 2017

My early impression--subject to revision--is that my Gen 2 does a worse job "holding" EV miles than my Gen 1 using it on the same commute.

I can't figure out if Gen 2 tries to "get back" to the held SOC setpoint, especially if it requires battery power beyond the ICE alone. On my Gen 1, the ICE (mostly) added charge to maintain the HOLD setpoint--but it also operated in a serial hybrid capacity. On my Gen 2, it seems that whenever it needs battery + ICE (like hard acceleration), it doesn't try to "replace" it. Maybe a characteristic of the parallel hybrid setup? Or maybe it tolerates more deviation?

It seems this member also noticed this issue on a 2000-mile trip where he used "hold" the whole time and lost half his EV miles. http://gm-volt.com/forum/showthread.php?284690-Questions-about-Hold-mode

What's going on here? Is the battery just augmenting the ICE in Hold mode? Do I need to drive within the (lower) power demands of the ICE alone in hold to avoid drain? Under what conditions (if any) will Gen 2 maintain the Hold setpoint?

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Arcanox

· #2 · Oct 8, 2017

VoltenRock said:
My early impression--subject to revision--is that my Gen 2 does a worse job "holding" EV miles than my Gen 1 using it on the same commute.

I can't figure out if Gen 2 tries to "get back" to the held SOC setpoint, especially if it requires battery power beyond the ICE alone. On my Gen 1, the ICE (mostly) added charge to maintain the HOLD setpoint--but it also operated in a serial hybrid capacity. On my Gen 2, it seems that whenever it needs battery + ICE (like hard acceleration), it doesn't try to "replace" it. Maybe a characteristic of the parallel hybrid setup? Or maybe it tolerates more deviation?

It seems this member also noticed this issue on a 2000-mile trip where he used "hold" the whole time and lost half his EV miles. http://gm-volt.com/forum/showthread.php?284690-Questions-about-Hold-mode

What's going on here? Is the battery just augmenting the ICE in Hold mode? Do I need to drive within the (lower) power demands of the ICE alone in hold to avoid drain? Under what conditions (if any) will Gen 2 maintain the Hold setpoint?

I've never noticed mine losing miles in Hold mode. Whenever I use Hold, it will run the engine at a high idle when I'm coasting or close-to-coasting and the battery power gauge on the left goes down into the green while it returns to the setpoint. This only occurs after heavy acceleration. I've driven over a hundred miles in one Hold trip before and never lost a single mile of EV range.

Now, if you're driving up a steep slope such as a mountain the whole time, it's not going to have time to recover the lost mileage unless you drive flat or downhill for a while in the same trip afterwards. Note that the setpoint gets reset to the current SOC any time the vehicle enters Hold mode.

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Arcanox

· #15 · Oct 10, 2017

JRRF said:
No doubt that the implementation in G2 is an improvement. The bottom line is that the car needs it's battery under just about all circumstances. The concept of Mountain Mode is really a misnomer and designed to get someone thinking about this in the appropriate way. But the best way to drive the car is in Hold mode with a good deal of battery available for when it's needed (mountains or otherwise). If you are running low on battery, MM is there to help build it up -- since you need it all the time.

Reference the backfire issue in Hold mode when you have no battery left, it wouldn't surprise me if the engineers knew about this all along. The car can optionally run on engine, but it MUST have battery available all the time. If you are going on a long trip, be it to the mountains or the beach, you need to keep some battery in reserve. And if you run low, kick it into MM.

This highlights another point I've supported: that this car is not designed to be driven blindly.

I don't really agree with this. I'm guessing you probably have a Gen 1; the Gen 2 is designed differently and can really be driven as a normal hybrid without ever being plugged in or paying attention to the battery at all. Of course, why not charge it when you can? But in the Gen 2, the ICE should have plenty of power for climbing a mountain even with the EV range completely depleted. The engine is just as powerful as a Prius, and a Prius doesn't have any concept of mountain mode or anything.

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Arcanox

· #22 · Oct 13, 2017

Barry said:
I think it is possible that in hold mode, the car could be holding the same battery charge level in terms of percentage of full charge, but could also be displaying a lower range estimate due to having recent driving conditions that are less efficient. You could verify that if you access the charge level data through OBDII.

This is very true; I didn't actually think about that. If it's "losing miles" in Hold mode, chances are the short-term efficiency estimate was overly high and then now that you're driving at highway speeds for a while, the short-term efficiency estimate drops a lot and the range estimate drops without the actual SOC dropping.

When I drive home from work, there's about a half mile of me going 75-80 MPH before I exit (shortcut from my office complex to the nearest NS highway). Then I drive on a 45 MPH NS highway for the rest of my commute. My range drops about 5-6 miles in that short half mile stretch because I'm going so fast, then it hangs at that low value for several miles without decreasing further.

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Arcanox

· #25 · Oct 15, 2017

VoltenRock said:
I've seen this theory but not sure it's matched my observations. I watch the power flow display like a hawk (modern enhanced) and only see a change in EV miles remaining in HOLD when there is depletion (yellow) of the battery (like to assist the ICE on hills or hard acceleration). Similarly, there only ever seems to be an increase in EV miles remaining when there is green (like with regen or ICE). It doesn't seem to be related to driving style unless you are requiring a lot of battery assist to the ICE.

As an experiment, I did the same route yesterday in Mountain Mode instead of HOLD (I had 9 EV miles remaining)--same terrain, speed, slightly cooler temps. It held religiously at those same 9 EV miles for the entire 2-hour journey. Last time, I lost 2-3 miles in HOLD. Every time the battery would assist, the ICE later provided a little charge back to the battery. The MPG was the same.

Of course, without knowing the software algorithm, we are all left to speculate. I can only base this off equipment the car provides. If OBDII provides real-time battery SOC (I thought it did not, that it only provided the same estimates the car makes) then this would add some more information. Either way, my early observations seem to show that the Gen 2 is less diligent about maintaining the battery in HOLD.

OBDII reports the raw battery SOC from 0-255, with 0 being absolutely 0 kWh, and 255 being a complete 18.5 kWh (so, you'll never see within 20-30 of either limit being reported back). It'd be easy enough to open Torque, have a SOC gauge, and throw the thing in Hold mode while on the highway to see if the SOC actually constantly decreases.

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Arcanox

· #27 · Oct 15, 2017

dolinod said:
Interesting thread. I wonder--does this have any implications for when the battery is empty? I imagine that when the engine comes on due to an empty battery, rather than the user-selected hold mode, it would need to have a tighter "grip" than if there is a generous battery reserve. Have any other users noticed a difference in how the car runs between the two modes?

I get better gas mileage in Hold mode than in CS mode, but I've never lost miles in Hold mode before. It will rev the engine up much sooner and faster in CS mode if the battery is super low.

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