GM Volt Forum banner

1 - 20 of 30 Posts

·
Registered
Joined
·
2,632 Posts
Discussion Starter · #1 · (Edited)
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
 

·
Registered
Joined
·
323 Posts
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.
 

·
Registered
Joined
·
1,251 Posts
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.
 

·
Registered
Joined
·
452 Posts
Rusty: it is posts like this that make this such a valuable forum. Thanks.
 

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

P
 

·
Registered
Joined
·
2,632 Posts
Discussion Starter · #6 ·
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...
 

·
Registered
Joined
·
2,632 Posts
Discussion Starter · #8 ·
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...
 

·
Registered
Joined
·
733 Posts
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.
 

·
Registered
Joined
·
1,916 Posts
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.
 

·
Registered
Joined
·
144 Posts
When I left home and knew I would be going up a 4 mile 7-8% grade (2600 ft) in about 15 to 20 miles distance I put it in MM with 23 miles showing on the batt. As soon as it went into MM the batt range dropped to 13 miles left and just before I got to the mountain section it started the ICE and I had very good power all the way up. At the top I put it back into normal and it showed 6 miles batt left.
 

·
Registered
Joined
·
571 Posts
Great info, I guess planning ahead is important in the use of MM.

Thanks,

P
 

·
Registered
Joined
·
706 Posts
Fellas,

If you know your going to need MM, why wouldn't you engage it before you pull out of your driveway?

Yes the car will go into CS mode sooner, but the ICE won't need to rev to build up the buffer -- it will be there already. It is much more efficient to charge the battery with grid power than to use the ICE to do it. So once in CS mode, the Volt will operate normally to maintain the battery SOC at the required MM buffer -- no high reving required until you start climbing. Once you get to the top, then you can put it back in normal mode and use up that buffer that you no longer need.

This should result in a better overall trip MPG because you're not using the ICE to first charge the battery back up to the required SOC (i.e., run it at max RPM) before you begin your climb (and continue to run it at max RPM) once you start climbing -- it's more efficient to simply maintain the charge before you get to the hill, and keep the ICE in it's sweet spot. Once you start climbing, the ICE is going to suck gas (high RPM) regardless. I would think the goal to maximize efficiency is to minimize the time the ICE runs at high RPM.

Cheers!
 

·
Registered
Joined
·
706 Posts
Exactly, that work too...the trick is keep the SOC in the Volt's battery high enough so that the ICE isn't requied to recharge the battery when you go into mountain mode....it just goes into CS mode sooner
 

·
Registered
Joined
·
2,632 Posts
Discussion Starter · #15 ·
If you know your going to need MM, why wouldn't you engage it before you pull out of your driveway?
When I first scaled those mountains for the big trip, that's exactly how I used MM. Hit MM out of the driveway, and the ICE started up near the foot of the mountains to maintain MM SOC. Had no trouble, and the engine didn't go crazy going up the hills. On the way back, hit MM just inside of El Centro (about 30-40 miles east of the grade?). I was already in CS mode, so the ICE had to charge up to MM SOC. But it was able to do so on flat land. By the time I hit the grade it'd been in MM SOC for a number of miles.

If you want/need full MM SOC, start early. There's no cost to it compared to "just in time".
 

·
Registered
Joined
·
1,251 Posts
No problem using MM early if you are using Cruise Control. The pedal seems harder to push in MM, so it's not as fun as sport or normal when your foot is on the pedal. One benefit is the extra battery power at the destination. Allows for quiet arrivals and departures without the ICE turning on.

If I had my choice, it would be that the navigation would automatically determine SOC based on route planning and speed. Being able to optimize speed and quiet operation would be ideal. Maybe in the Cadillac version with radar cruise control.
 

·
Registered
Joined
·
323 Posts
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.


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.
View attachment 909
If you look at the truth table for clutch operation there is one mode that is called "Transition". In that mode all the clutches are open. I could believe that when going thru this mode when going from one configuration to another, at load, that you could feel what would seem like a shift. Care to come in on this ***?
 

·
Premium Member
Joined
·
14,156 Posts
Where is the app when you need it?

If you know your going to need MM, why wouldn't you engage it before you pull out of your driveway?
That's a valid point, but the big question in practice would be how to know if you would "need it". That would of course depend on the topography. If you had a long flat and then a lot of downhill before the climb you might not want to turn it on at all if regen would provide all the reserve necessary for the latter climb. Or you may not as much reserve as you think. On the climb from El Centro Rusty is describing I would love to go 80 MPH but the reality is that there are too many slow trailers to do that. The best way to put this is that, if you don't need MM, then there can be a cost using it since the best strategy would be to end up with a flat battery rather than a reserve you didn't need. In this latter case you would be charging from the genset rather than from the grid which isn't ideal.

It would be tres cool if you could plot your route and the car would look at the profile and tell you when you should use MM. Is there an app for that? ;)
 

·
Registered
Joined
·
2,632 Posts
Discussion Starter · #19 ·
If you had a long flat and then a lot of downhill before the climb you might not want to turn it on at all if regen would provide all the reserve necessary for the latter climb.
*heh*... The lead up to that particular mountain is a long drive gradually up hill from *below* sea level. Regen need not apply! :)

On the climb from El Centro Rusty is describing I would love to go 80 MPH but the reality is that there are too many slow trailers to do that.
If you can take that hill on cruise control at 80 MPH in a Volt, ignoring the drive train, you're a better man than I! The first time I took that hill in my Volt, returning from Texas, I hit it in MM with the cruise control set at 70. Many of the turns are marked for 60. Taking them at 65 is easy in a Volt. After 3500+ miles of driving, taking them at 70 was more annoying then I liked.

If you can take that entire hill at 80, I'll be quite impressed indeed!
 

·
Premium Member
Joined
·
14,156 Posts
If you can take that entire hill at 80, I'll be quite impressed indeed!
I don't know if I could because I've never gotten a chance. There are always a bunch of trailers hauling desert toys coming back from Glamis. As I remember there are a couple of curves about half way up, sort of a separated S, where you'd have to slow down, but otherwise 80 should be doable.

At least in the car I have. No idea about the Volt. Actually I think of the Volt as being more an in-town vehicle so I'm not sure I'd want to drive it long distances.
 
1 - 20 of 30 Posts
Top