Do we really need Mountain Mode?

[Rusty]

I'm planning a San Diego to Laguna (6000' climb) to Julian then down the hill to Scissors Crossing and back up the east side of 8 all on normal mode to check it out.

I think the car'll do that, and if so the only need for MM for 95% of Volt drivers is EV demos.

So I tried that today. Some 230 miles later, the answer is absolutely positively unequivocally "maybe."

For freeway driving, all driving was cruise control at the speed limit. For mountain driving it was sane turns, and not above speed limit. Climate control was 8% (fan only) during the climbs. Temps ranged from 60 in the hills to 78 on S2.

Dropped into CS mode just before I got to the 1000' mark on the climb out, and just before hitting 4000' for the first time after about 17 miles (4% average grade on the slope part, but "lumpy") the "reduced power" warning sounded. BUT! Right after that there's a small valley before the first crest, then a big valley.

Car did fine, and had no trouble maintaining 70 MPH. The warning went away after the first crest, and that drop to 3500' at Diablo canyon. It didn't come on again up to the Sunrise Highway turnoff at 4100'. In fact the engine fully idled down at the stop sign at the end of the ramp (I had a wait for a Prius coming off the mountain to turn across me, driver and passenger STARING at the Volt as they went by :-).

The 2000' mountain climb up Laguna at 35-55 MPH over 8 miles (5% grade) had no trouble. Engine stayed at normal max RPMs the entire climb, and having reset a trip odo at the bottom observed 15 MPG for the duration. The little 1.4L can suck gas!

The climb back up the other side of the hill, from the S2/I8 intersection in Ocotillo west was a different story. Starting at 400', there's a direct climb of ~3000' straight up over 13 miles @65 MPH (4-5% grade, with no "lumps"). Just before making the first peak the warning came on, and sure enough speed started to drop. Came down to 60 (which actually was the limit in that turn) as I rounded the top, and stayed on as I got to the flat and the first valley.

However, it let me accelerate to the new 70 MPH limit without complaint. It made the 6 mile 1400' and 9 mile 1000' climbs with no complaints.

So, for these trips all in all the car performed perfectly acceptably without Mountain mode. With climate or more vehicle load? No, I'd use Mountain Mode for any solid climb over 2000'. Less if steeper.

Interesting observation: A few miles before each of the "reduced power" warnings, the car shifted. I don't know what it shifted from or too, but there was a momentary loss of engine power (and the engine actually spun down a bit) then a re-engage. I'd say it was around 150 milliseconds, give or take 30.

It happened again at 55 MPH on the climb up Laguna, but only about half a mile before making the first (flat) meadow. Likewise it happened at 70 MPH just before making the highest peak at the Golden Acorn on the return trip. In addition, it did it again on a flatish part just after that peak.

Another interesting (well, to me at least) observation: If you've taken a normal depleted SOC car, put it in MM, and floored it off the line, you know what the highest engine rev the car normally will make, right?

After those shifts the engine ran *quite* a bit faster than that! And it stayed there, even for a little bit after normal power was returned. It was WHINING loud!

At four of five of the times the car "shifted" it was under a heavy torque load climbing a steep hill. What I suspect is that as the SOC dropped and the car prepared for reduced power, it declutched the engine (and generator) from the ring gear so that it could run the generator at *above* the max RPM allowed on the ring gear. If so. apparently it can't do that while there's torque going through the clutch, so it neutrals for a moment, declutches, then goes into hyper drive.

Interesting experiment. I don't plan on doing it again.
topo.jpg

[Xzlon]

My fisrt impression of the Mountain Mode is that it should only be used for high speed travelling up a steep grade. I have about a 3000 foot elevation change in 20 miles to my home in the hills. So the first time up I ran in mountain mode to 15 or 20 minutes before starting up the hill and left it in mountain mode till I got home. When I checked I had 6 miles of EV range left after I got home. Ideally it would be zero miles left to preserve gas. No power problems on the hill. So I thought do I start using MM later or switch back to Normal six miles before arriving at home?

The next time in about the same circumstances I did not use MM at all. I made it about 2/3 of the way before CS kicked in. Still had plenty of power for travelling up the hill at 40 to 50mph (which is the normal with the corners involved). I used .26 gallons of fuel in the last few miles while in CS mode.

In fact one thing I really like about the Volt is with constant accelerator pedal position it slows down very little on short grades. Almost like the pedal sets speed and not power. The power is changed automatically to maintain speed and there is no real feeling of a need to force a down shift like with my Buick LaSabre. For feel the Volt is closer to the feel I had with my supercharged Pontiac Bonneville SSEI than with the Buick. So far I really love the Volt for uphill and downhill driving.

[Mark Z]

The grade out of Baker when traveling east to Vegas requires Mountain Mode about 10 minutes before Baker if you want to maintain 80 mph over the pass. By turning MM on at Baker, the Volt dropped to 68 mph for about the last 3 miles of the grade. Add A/C and/or passengers and the results will be different.

[honoreitiscom]

Rusty: it is posts like this that make this such a valuable forum. Thanks.

[PatsVolt]

Just wondering, did you allow 20-30 min. for the system to build reserve in the battery in MM?

P

[Rusty]

Just wondering, did you allow 20-30 min. for the system to build reserve in the battery in MM?

Are you asking me or Mark Z? I very specifically did not use MM at all for this testing. I believe Mark Z's comment is that he's only building up enough MM buffer to make it *just* over the particular pass in question. The whole point of MM is you don't want to use it any more than you have to.

For my testing today I would have only needed a few minutes of MM charging, but I don't know how well using it at the bottom of the hill would help (and I'm not in a mood to test it at the moment). What I think would work better is MM to just enough to build the needed reserve SOC for the grade, then HOLD. That way I could have sufficient reserve for that last little bit.

Yeah, I know. No HOLD mode...

[Koz]

Rusty: it is posts like this that make this such a valuable forum. Thanks.

Agreed. Excellent writeup. It would make a great lead story on the home page.

[Rusty]

It would make a great lead story on the home page.

Oh ducky, what have I gotten into now? I think it would need to have the speculation at the end removed or resolved before going there...

[twist]

Held the Volt at 67mph in Normal mode as it switched off battery power into CS mode. The 1.4L started and was running at a fairly low rpm. Sounded like 2000rpm. Without accelerating I entered Sport mode. The 1.4L rpm increased to about 3000rpm. Sport mode is in effect Mountain mode lite.

[Koz]

Oh ducky, what have I gotten into now? I think it would need to have the speculation at the end removed or resolved before going there...

RU kidding, that's the best part. Nothing wrong with speculating on an obsevation as long as it's presented as such. It sure would be interesting to know if the engine/generator was engaging with or disengaging from the ring gear with that "shift". I would guess it is engaging in preparation power reduced mode (no/little battery contribution). The increased RPM is could be from the ring gear requirement for the current spead. It would be easy to tell if this accurate if "shifts" were induced at noticably different speeds.