Mountain Mode not needed (Gen 2)

6076 Views 25 Replies 11 Participants Last post by wordptom, Oct 5, 2018

obermd

Discussion Starter · Oct 1, 2018 (Edited)

It's leaf peeping season in Colorado, so this morning I filled my tank and headed for the mountains. I live at 5,700 ft above sea level and ran out of battery after a little over 47 miles and a net climb of 2,800 ft. I stayed in Normal mode the entire loop, driving over Kenosha Pass at 10,000 ft, Independence Pass at 12,095 ft, Vail Pass at 10,662 ft, and through the eastbound bore of the Eisenhower tunnel at 11,158 ft. I drove the posted speed limit the entire way and kept my Volt in Normal mode the entire time. Kenosha, Vail, and Eisenhower approaches are posted 65 MPH. Kenosha isn't that steep so my car was only pulling about 20 KW on the climb. Climbing Vail and Eisenhower my car was running about 40-45 KW power output and the ICE was happily screaming along. I was even able to accelerate up both passes to about 80 MPH using the Normal mode "low" buffer in the battery. The descent from Independence Pass to Aspen actually resulted in three bars of power being regenerated. When I got to down to Georgetown I got off I-70 for a bathroom break and had one bar of battery from the descent. My car correctly identified it as "gas" power and allocated it to the gas fuel economy number even after I restarted the engine even though the Classic Enhanced display showed battery power only upon restart.

Here's the Energy Usage display when I got home.

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The leaves were stunning with a variety of greens, yellows, and reds throughout the drive.

One other note: I was passed on I-70 by a CDOT (Colorado Department of Transportation) painted Chevy Bolt. Interesting...

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obermd

Discussion Starter · #3 · Oct 1, 2018

jcanoe said:
Did you drive in D or L for the ascents and descents?

Both. I prefer D for most of my driving but using L allows me to set the cruise control and not worry about my speed. I was in L almost the entire way back across I-70; L + cruise => set and forget it when it comes to speed. I used D for any driving I wasn't using cruise control for because I find L to be too jerky for my liking. The CO-82 descent from Independence Pass to Aspen is posted 25 to 35 MPH depending on the section of road and I used L for this entire 3,500+ ft descent with short stretches of shifting into D to allow my car to accelerate back to the posted speed limit without touching the pedals after having to slow down for excessively sharp corners or other road hazards. The first 15 miles of this descent was almost a pure zero-pedal drive where I used L+cruise control to maintain speed, L+regen to slow down, and D+gravity to accelerate. I had to use the brakes twice to come to a complete stop due to it being a 1 lane road for about a mile.

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obermd

Discussion Starter · #8 · Oct 1, 2018

Barry said:
Interesting and impressive results. I wonder if mountain mode might be more necessary on certain kinds of climbs, maybe where you have a lot of tight switchbacks and you would be accelerating out of the turns frequently, while also climbing-- especially if you were in a hurry. I think Pikes Peak is like that (I have not driven it, so not sure).

The big issue with this theory is the posted speed limits on roads like this tend to be 35 MPH or lower. I've seen some in Colorado where the switchbacks are so frequent and sharp the posted (white sign) speed limit is 15 MPH. On the other hand, the Volt is definitely not the car I'd want to enter in the Pikes Peak Hill Climb simply because you do have a lot of slow hard turns followed by hard acceleration. The Naturally Aspirated ICE in the Volt simply wouldn't have enough power to maintain the battery SOC and the battery is probably too small for this type of driving. On these two climbs there was enough battery SOC to accelerate from 50 to 70 MPH going up Vail Pass after passing a car that had just passed a semi and the from 50 to 80 MPH going up to the Eisenhower Tunnel after to get out of a three lane jam of slow cars. In both cases I resumed the cruise control and let my car slow back down - the Colorado State Police actually monitor the three lane climb to the Eisenhower Tunnel for aggressive driving and I actually did see someone pulled over about two thirds of the way up to the Tunnels.

Barry said:
I think carrying a maximum load would make a difference as well. Auto makers have to design everything around the maximum gross weight even though most of us rarely or never load a car that much. Gross weight doesn't matter much for cruising on a level highway, but for climbing and accelerating, it is a larger consideration.

I had a similar thought driving across the high desert valley between the east end of Glenwood Canyon (6,000 ft) and Avon (7,400 ft) at the posted 75 MPH. In fact, based on prior experience in Kansas at 75 MPH where Mountain Mode was 100% depleted I wasn't sure the car would maintain the "empty" SOC in preparation for the actual Vail Pass climb that starts only a few miles east of Avon (Avon is west of Vail). Battery's SOC for "empty" was apparently maintained and I had sufficient battery power on both approaches to accelerate between 20 and 30 MPH. The battery portion of the power meter reached 100KW on both those accelerations.

Based on the power differences I've seen when I'm alone in my Volt vs. when my wife and I are travelling together with a fully load cargo area/back seat I suspect the ICE is still powerful enough by itself to not require Mountain Mode. Remember, the Volt's ICE is Naturally Aspirated (NA) and I took the car up the steep approaches to the two highest points on the US interstate system at 65 MPH and it didn't miss a beat. The ICE screamed but didn't miss a beat and wasn't maxed out on the power meter

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obermd

Discussion Starter · #10 · Oct 2, 2018

jcanoe said:
Unless there is sufficient battery SOC to provide additional power the Gen 2 Volt is capable of generating up to 48kW output via motor generator A (MGA) when the ICE is running.

I figured it was 50KW based on the Classic Enhanced display. I still think my Volt would be good to go even fully loaded over I-70 as the added weight isn't that much as a percentage of total vehicle weight. I have basically stopped using Mountain Mode unless I want to recharge for short range (5 miles or so) off-highway driving in the middle of a trip.

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obermd

Discussion Starter · #12 · Oct 2, 2018

wordptom said:
That’s a fascinating energy usage display that shows the Volt calculations are completely ignoring the energy content of any regen you created and used on this trip.

The Gen 2 window sticker rates the car at 106 MPGe, i.e., it can travel 106 ev miles using the energy content of 33.7 kWh of power from the wall (= energy content of 1 gallon of gas = 1 Ge). The 53 ev miles per charge rating indicates one full charge uses 16.85 kWh, or 0.5 Ge, from the wall.

On this trip, you drove 47.3 miles on the full charge, using 0.5 Ge of electric fuel from the wall, and the display shows your Trip MPGe = (47.3/0.5) = 94.6 MPGe.

You also drove 340.4 miles using 6.74 Ge of gas, for a total of 387.7 miles using (6.74 + 0.5 =) 7.24 Ge of energy equivalent fuel. The display shows your combined trip MPGe = (387.7/7.24) = 53.6 MPGe.

The energy content of the regen you created and used during the trip is clearly not factored into the energy usage display numbers at all.

Except I think it was - anytime I was descending steep enough grades I saw negative numbers in the KW meter and no gas usage for a ways after those descents. The 1.5L engine is rated 42 MPG on the highway and I have good reason (two round trips from Denver to New England) to believe that number is accurate. The only way to get the 50.6 MPGcs number shown is if the car is running on regenerated battery power for 65.5 miles. This means I regenerated and used 15.7 KWh of power on those downgrades, all of which was reported in the MPGcs number.

340.4 miles ICE / 42 MPG EPA = 8.10 gallons.
Subtract actual gas usage of 6.74 gallons to get 1.36 gallons.
Multiply 1.36 and 42 to get 57.3 miles driven on regenerated power. Using straight ratio calculations for

53 miles 57.3 miles
--------- = ------------
14 KWh regen KWh

results in 15.14 KWh of usable regenerated power during my trip.

The Volt really needs a third number showing how much power has been regenerated during ICE operations. This number is hidden in the gas usage in the form of miles[SUB]cs[/SUB] incrementing but no gas being used.

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obermd

Discussion Starter · #15 · Oct 3, 2018

Barry said:
I think you are trying to count the regen electricity wrong. The only energy inputs into the car are gas and the grid electricity that is supplied by an EVSE. The regen is not an energy input into the car. It is just the temporary storage of momentum or potential energy that came from either gas or grid power.

To look at it another way: Imagine the battery is empty and you drive to the top of a mountain using gas. Then you drive back down the mountain and regen puts 5 kWh of electricity into the battery. Where did that 5 kWh come from? It came from the potential energy of the car being on top of the mountain. What put that potential energy into the car in the first place? The gas used to drive it up there. Therefore, that regen electricity is really just energy from gas. When you drive off that 5 kWh, you are driving on the energy from the gas, so it is counted as gas miles. No need to separately measure regen energy.

The initial EV miles was about three-quarters of a gallon equivalent short of what I normally get this time of year. It's because of the 2,800 ft elevation gain through Jefferson County. So a small part of my regen was counted towards gas when it really should have been counted towards the EV range.

The bottom line is not only is this car more efficient than the EPA number suggest but the ICE power plant has a lot more power than it's given credit for. In addition, based on my experience Mountain Mode is useless if you're driving much over 70 MPH for any extended time as the car will periodically draw on the battery but never recharge to the MM set point and not really needed for high altitude driving where a non-turbo/super charged gas engine struggles for lack of oxygen.

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obermd

Discussion Starter · #19 · Oct 3, 2018

ItsNotAboutTheMoney said:
Mountain Mode was already there, so I guess they just left it.

But, report back on how it goes if you do the same trip in winter on snow tires.

CO-82 will be closed. The rest of the roads will be bumper to bumper ski traffic

so you still won't need Mountain Mode. I might run in hold mode just to get better heat in the cabin though.

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obermd

Discussion Starter · #20 · Oct 3, 2018

ItsNotAboutTheMoney said:
Mountain Mode was already there, so I guess they just left it.

That's actually my suspicion as well. It does have another use though - after you've driven out of battery on the highway it gives you a way to get some battery back for when you leave the highway.

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obermd

Discussion Starter · #24 · Oct 5, 2018

Nanabanana said:
I really need to learn how to drive my Volt. You folks have opened my eyes. I have been driving my car since 2012 and I rarely use L or switch back in forth between the 2. Can you do this while you are moving? Wouldn't it damage the transmission. Obviously I have a Generation 1. I live 1.3 miles from my job. I drive to and from everyday. I do take my grandson to school and pick him up from afterschool daycare. And what is ICE? I am really not knowledgeable about this machine. I love my car. I hit a deer at 77 mph 2 years ago. I was driving at night. This care saved my life. It is a tank! Cost to repair was a little over $5,000.00. But it looks brand new. It hit the right front quarter panel. right where the inverter is. I need to read my manual so I know what my full capabilities are for EV use. I have 47,462 miles on the car. It is 6 years old.

I frequently switch back and forth between L and D. All these two gear positions do is tell the ECU how you want the car to respond to no throttle to make the car act like an ICE slushbox in the same L & D gear positions.

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