Feb 22

Climbing a 5-percent grade at 65 mph in extended-range mode

 

By George S. Bower

Note: The data acquisition done for this article pertains primarily to a 2011-2012 spec Volt with 16.0-kwh battery, but loosely applies to the very similar 16.5-kwh 2013 also.

How low will the battery go?

 

We know that the Volt’s 1.4-liter internal combustion engine (ICE) makes less horsepower than is required to climb a steep grade so we need battery power to maintain speed on some hills depending on grade and vehicle speed.

Normally the Volt uses 21.9 percent to 86 percent state of charge (SOC) of its 16 kwh battery. In EV mode, when the battery gets to the bottom of its usable range (21.9 percent SOC), the ICE starts and immediately tries to build a small buffer to use as back up. This buffer is .25-.40 kwh which is a fairly small amount.

IMG_3242
 

What happens if we start climbing a hill that requires more HP than the Volt’s ICE can supply and we are already at 21.9 percent? Obviously we start draining the battery below 21.9 percent.

How far down will it drain and how long will it last?

In order to investigate, I took data using my DashDAQ up a hill that I drive routinely between my winter house in Tonto Basin, Ariz. to Payson, Ariz. For this test, I timed it so that the HV battery ran out and Volt switched to extended range mode at the bottom of the hill. My cruise control was set at 65 mph for the entire climb of 5.87 miles and 5.33 minutes. The resulting data is shown in figures 1 and 2.

Fig1
0000055654-Slide2
 

We can see at the bottom of the hill right after going into extended-range mode (power split) and before the hill gets very steep that the Volt starts to build its .25-.400-kwh buffer as a reserve but soon the battery starts to deplete because of the steepness of the hill.

Initially the ICE is at 2,700 RPM but as the battery SOC drops lower and lower the Volt raises engine rpm to keep the buffer from running out. By the end of the climb, the buffer has gone to -0.7 kwh and the ICE speed has increased to 4,300 RPM. This -0.7 kwh is equivalent to a 17.5 percent SOC. I was not able to fully deplete the battery in this test. If I had, the Volt would have gone into “Propulsion Power Reduced” mode and would have slowed down. According to Walter Crowe (saghost on the GM-Volt forum) this battery “floor” occurs at 15 percent SOC.

At the rate I was depleting the battery, Propulsion Power Reduced mode would have occurred in another 3 minutes (3.33 miles) which would have given a total endurance of 8.37 minutes and 9.2 miles before the battery hit the floor.

Volt pulls a surprising shift toward the end of the climb

 

Usually when the Volt shifts planetary gear set configurations, it is so subtle that the driver does not even notice that the shift has occurred. However, not in this case as I remember feeling the shift when I was taking the data and did not know what had happened until I reduced the data.

The shift is shown in figures 1 and 2 at 300 seconds. At this point in time the Volt shifted from power split to series mode. A detailed look at the planetary gear set configurations before and after the shift is shown in figure 3.

0000055654-Slide3
 

In power split, note the high NEGATIVE speed of MGB (-3,597 rpm). MGB is making power and feeding it to MGA. MGA is also taking power from the battery and ICE and MGA power is being fed back into the ring gear.

In series mode, MGB is at even higher POSITIVE speed (6,078 rpm) driving thru the sun gear to the wheels while the ICE and MGA are independently making electrical power and sending it to MGB. MGB is also taking power from the battery.

But why the shift?

 

I do not know. I would have expected the Volt to stay in power split all the way up the hill but it did not. I can only speculate as to why the Volt shifted into series:

1) Volt wants to be in series mode when “Propulsion Power Reduced “ sets in.
2) Volt wants to be in series mode when climbing hills because of the numerically higher gear ratio of 3.21 sun to carrier vs. 1.45 ring to carrier in power split.

If reason 1 is why it shifted, why didn’t it wait to shift until it was closer to the battery floor?

If reason 2 is why it shifted, then why did it wait so long to shift?

Any ideas?

This entry was posted on Friday, February 22nd, 2013 at 5:55 am and is filed under General. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

COMMENTS: 113


  1. 1
    Eco_Turbo

     

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    Feb 22nd, 2013 (7:15 am)

    Interesting test George, reminds me of the time I was able to “feel” the power of the short body big block roadster I had, going up a steep mountain hill in second gear. Do you think letting the battery go all the way to the floor might be where the extra range of the 2013 Volt comes from?


  2. 2
    Dave G

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    Feb 22nd, 2013 (7:33 am)

    For the shift near the end, I would guess that the series mode is more powerful but less efficient.

    In normal cases, the software favors fuel efficiency. When the battery starts getting very low, the software favors max power.


  3. 3
    Mark Z

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    Feb 22nd, 2013 (7:35 am)

    George, excellent report, graphs and photo. Reminds me of the 17 mile Baker, CA grade of 5 to 7% driving to Vegas. I failed to use Mountain Mode soon enough and the 2011 Volt dropped speed during Propulsion Power Reduced mode.

    My wild guess is that GM wants more engine power for battery generation than propulsion on the hill climb. As the approach to PPR is close, the change occurs to improve propulsion since there is no longer enough SOC to maintain speed. GM would be able to calculate what the PPR speed should be under those conditions before actually limiting the speed to the calculated amount.

    I have emailed my nephew who owns a Volt for his thoughts on the subject. With your weekend report, it gives extra time for careful consideration, opinions, and answers.


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    Walter

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    Feb 22nd, 2013 (7:38 am)

    GM revised the battery chemistry slightly, resulting in more chemical capacity from otherwise identical cells. (Hence 16.5 kWh instead of 16 kWh nominal capacity.) This extra capacity is responsible for the longer range, not anything to do with the floor. George put that disclaimer in because we think the ceiling and floor are at the same voltages/absolute energy remaing, but they aren’t the same percentage on a 2013 because they added that half kWh to the central operating range.
    Walter


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    Dave G

     

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    Feb 22nd, 2013 (7:47 am)

    From the article: My cruise control was set at 65 mph for the entire climb of 5.87 miles and 5.33 minutes.

    This seems like an unusual stretch of road. In my experience, roads with a 5% grade lasting that long usually have some curves that force you to slow down.

    What is the posted speed limit?


  6. 6
    Dave G

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    Feb 22nd, 2013 (8:01 am)

    Mark Z: Reminds me of the 17 mile Baker, CA grade of 5 to 7% driving to Vegas. I failed to use Mountain Mode soon enough and the 2011 Volt dropped speed during Propulsion Power Reduced mode.

    Right. With the recent Model S New York Times article, it’s important that visitors to this site understand: The worst thing that will happen is you’ll have to slow down a little.

    To further clarify, in this case, how much did you have to slow down?

    As a side note, I usually use Hold Mode for long distance road trips, and only use up the battery near the end, so I have full battery power for climbing hills.


  7. 7
    Mark Brooks

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    Feb 22nd, 2013 (8:15 am)

    Humm, nifty data, have you tried this in mountian mode yet? It would be great to compare the data side by side for a base line. Keep up the testing!


  8. 8
    George S. Bower

     

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    Feb 22nd, 2013 (8:21 am)

    Dave G:
    For the shift near the end, I would guess that the series mode is more powerful but less efficient.

    In normal cases, the software favors fuel efficiency.When the battery starts getting very low, the software favors max power.

    I believe this is born out in the graphs. After the shift battery drain actually increased. Note the current increase from the battery in series mode in figure 3.


  9. 9
    statik

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    Feb 22nd, 2013 (8:24 am)

    /wave to George

    I’ve mused this very same issue myself on more than a few occasions (and what was going on behind the scenes), but never considered putting the amount of time and research you have into sussing out the results.

    Appreciate the article George! And having done a little writing myself, I especially appreciate the amount of effort I know goes into working up something like this for the readers.

    …nice work, +1


  10. 10
    Walter

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    Feb 22nd, 2013 (8:26 am)

    Dave G:
    For the shift near the end, I would guess that the series mode is more powerful but less .

    In normal cases, the software favors fuel efficiency.When the battery starts getting very low, the software favors max power.

    The *electric motor* is more powerful in series. The car actually had less ability to deliver engine power to the road in series (because it all has generator/motor losses attached.)

    The most striking point IMO is that after going into series, the car didn’t rev up any further. In fact, of you look at the two state charts George provided at the end, you’ll note that the car is actually using 50% more battery power after the series switch – from 18 amps (~6.5 kW) to 26 amps (~9.4 kW) – presumably to make up the increased conversion losses.

    So if it’s delivering the same power less efficiently, why do it? My guess is that PPR is always in series for better control off the power flow, and that George got low enough to brush up against the edges of it. Switching modes always requires the car to be driven electrically for a few seconds while the ring gear is starting or stopping, so GM must have saved a little power to get you in over the hard limit.

    The other thing I think is really interesting is that we never see 4800 rpm here. If the car is doing what we think, it’s right on the edge of pulling back power to protect the battery, but the engine is stabilized at 4300 rpm, not the 4800 that GM said provides rated power.
    Walter


  11. 11
    Mark Z

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    Feb 22nd, 2013 (8:27 am)

    Dave G: …To further clarify, in this case, how much did you have to slow down?…

    From a 1-21-2011 post:

    “Drove the Volt to Vegas for CES and everything went smoothly. The grade out of Baker requires mountain mode about 10 minutes ahead of time or the 80 mph will drop to 70 near the top. Very pleased with the comfort, ride, handling and performance. A great car!”

    I remember the Volt dropping to 65 mph near the summit. I had a passenger who rode with me to CES in the Volt. This year he refused to ride in the Tesla due to a imagined extended delay at the SuperCharger. He drove his ICE vehicle instead!

    BTW, Volt drivers now pass me on the freeway as I drive just above the speed limit to avoid tickets. Driving slower also helps the BEV maintain charge. I may be able to pass you on a hill, but you will get to your final destination faster in a Volt!


  12. 12
    George S. Bower

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    Feb 22nd, 2013 (8:31 am)

    Dave G: This seems like an unusual stretch of road.In my experience, roads with a 5% grade lasting that long usually have some curves that force you to slow down.

    What is the posted speed limit?

    Mark Brooks:
    have you tried this in mountian mode yet?

    Yes but not w/ DashDAQ taking data.

    I would like to rerun the test twice. First at a higher speed of around 70 in an attempt to get into PPR. It might give us some clues as to the reason for the shift.

    second test would be in MM just to observe the subtle differences in programming GM may have incorporated. For example, since we have more battery to eat into, they may change the rate at which they ramp the ICE speed–ie ICE speed might not be as high.


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    kdawg

     

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    Feb 22nd, 2013 (9:13 am)

    Walter: GM revised the battery chemistry slightly, resulting in more chemical capacity from otherwise identical cells. (Hence 16.5 kWh instead of 16 kWh nominal capacity.) This extra capacity is responsible for the longer range, not anything to do with the floor. George put that disclaimer in because we think the ceiling and floor are at the same voltages/absolute energy remaing, but they aren’t the same percentage on a 2013 because they added that half kWh to the central operating range.

    Using my Torque AP, my 2013 Volt has gone down to 19.5% on the expressway (flat), before the ICE would start building the buffer back to 21%.


  14. 14
    George S. Bower

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    Feb 22nd, 2013 (9:15 am)

    statik:

    Appreciate the article George! And having done a little writing myself, I especially appreciate the amount of effort I know goes into working up something like this for the readers.

    Thanks for stopping by!


  15. 15
    joe

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    Feb 22nd, 2013 (9:18 am)

    (click to show comment)


  16. 16
    Charlie H

     

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    Feb 22nd, 2013 (9:24 am)

    George,

    What is the actual change in altitude over that stretch?


  17. 17
    George S. Bower

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    Feb 22nd, 2013 (9:32 am)

    Mark Z: From a 1-21-2011 post:

    I remember the Volt dropping to 65 mph near the summit.

    I just ran the numbers for what speed the Volt would have gone to using my computer model and I am getting 56 MPH.

    I show a road load at the tire of 67 HP for this grade and speed (which was 6.3% grade for the last part of the hill) at 65 MPH. We see from fig 2 that the Volt is drawing 7 KW from the battery at this point. (7 Kw=9.4 HP). So then all I did was reduce speed in the model until my road load went down from 67 HP to 57.6 HP.

    Resultant speed was 56


  18. 18
    Jackson

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    Feb 22nd, 2013 (9:33 am)

    This reminds me a bit of the endless ” Pike’s Peak scenario” discussions we used to have here before the first Volt hit dealerships.


  19. 19
    George S. Bower

     

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    Feb 22nd, 2013 (9:33 am)

    Charlie H:
    George,

    What is the actual change in altitude over that stretch?

    It is shown on figure 1.


  20. 20
    Charlie H

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    Feb 22nd, 2013 (9:35 am)

    One thing that would make EV, PHEV and HEV operation more efficient would be topographically-aware navigation software linked to the SOC management. As George pointed the nose of his vehicle up that hill, the nav software could have told the SOC management how much altitude would be gained. The SOC management would have realized that SOC would go very low and could have directed the ICE to begin filling the battery right away.

    To do this, nav databases would also need altitude information about every hill, which is already available from the Feds but, so far as I know, not included in nav systems.

    Another potentially useful feature would be “fuzzy” cruise control. You set parameters like -5/+5 and dial it in to 65. Going downhill, the car would be allowed to maximize recovery of gravitational potential by speeding up. Going uphill, the car (especially an HEV) could be allowed to keep the engine in its most efficient range by losing a few miles per hour, hitting minimum desired speed at the peak of the hill. If the car “knew” that there was a long dowhill behind the peak, it could run the battery down to minimum SOC, knowing it could recover the charge using gravitational potential.

    It would be best to combine this with awareness of the traffic around the vehicle but that’s not terribly difficult, either. Radar cruise is already available on some cars… just add a transceiver in the tail.

    It could be that this wouldn’t have the savings I imagine… there’s the contants of rolling resistance and other energy demands but I think it has potential, although probably not as much potential as platooning.


  21. 21
    Dave G

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    Feb 22nd, 2013 (9:41 am)

    Mark Z: I had a passenger who rode with me to CES in the Volt. This year he refused to ride in the Tesla due to a imagined extended delay at the SuperCharger. He drove his ICE vehicle instead!

    For other BEVs (Leaf, Spark EV, Fit EV, etc.), this would be a non-decision. They have to use ICE vehicles for longer trips.

    So unless you’re wealthy enough to afford a Tesla, and like to spend time eating in out of the way places, pure BEV solutions still use some amount of liquid fuel.

    Since EREV and pure BEV users both drive the majority of their miles on electricity, the miles that use liquid fuel may run on something other than gasoline.


  22. 22
    Charlie H

     

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    Feb 22nd, 2013 (9:55 am)

    George S. Bower,

    Oh (slaps forehead). Thanks. I’d overlooked it.


  23. 23
    George S. Bower

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    Feb 22nd, 2013 (9:57 am)

    joe:

    What are we doing here, trying hard to find something wrong with Volt…

    Absolutely not. It shows the brilliance of GM’s engineers to include mountain mode in the design.

    Also I would say that it has a tendency to sway those that think a smaller range extender would be a good idea to reconsider their opinion.


  24. 24
    Mike

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    Feb 22nd, 2013 (10:10 am)

    Charlie H: One thing that would make EV, PHEV and HEV operation more efficient would be topographically-aware navigation software linked to the SOC management.

    An OEM calibrator explained to me that incorporating the NAV would make it part of the “emissions system” since it could control engine operation. That brings baggage they prefer to avoid, specifically with warranty requirements.

    That said, I could swear I read that BMW did something similar in one of their hybrids.

    Thanks for the taking the time to present this great data George.


  25. 25
    Loboc

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    Feb 22nd, 2013 (10:13 am)

    Nice work George! Makes waiting for my Volt even more difficult.


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    anthonykitmcinnis

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    Feb 22nd, 2013 (10:41 am)

    The things I learn about this car amazes me more and more each day.


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    Charlie H

     

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    Feb 22nd, 2013 (10:41 am)

    Mike,

    “Control” is such a harsh word. Let’s say it “makes recommendations.”

    This is rather too bad because in the case of the Volt or other PHEV, the Nav software could determine what it means to “go home” and could optimize management to run the battery down to minimum at precisely the moment the car enters the garage. It could understand other charge points, too. That would have reduce tailpile emissions.


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    Mike

     

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    Feb 22nd, 2013 (10:50 am)

    Charlie,

    I saw a Lutz interview years back where he suggested the Volt would do precisely what you suggest but it (apparently) didn’t get far past the theoretical stage.


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    kdawg

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    Feb 22nd, 2013 (11:00 am)

    joe: Why not simply call GM and find the correct answer and come up with the facts instead of speculating.

    I think I have Andrew Farah on speed-dial, hold on…

    (j/k)


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    steve

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    Feb 22nd, 2013 (11:11 am)

    George S. Bower: Absolutely not. It shows the brilliance of GM’s engineers to include mountain mode in the design.

    Also I would say that it has a tendency to sway those that think a smaller range extender would be a good idea to reconsider their opinion.

    Not necessarily, a smaller engine optimized for power generation might still be feasible. I recall someone at GM commenting that they could have gone smaller and more economical but it would have compromised how quite the car was. Considering the average noise level of cars we’re already driving now, if it sold at an appropriate price point, it would be a success. If I got better economy I might overlook not driving one of the most quite cars on the road. Heck I’m not driving anything exceptionally quite now.


  31. 31
    Dave K.

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    Feb 22nd, 2013 (11:16 am)

    What is even more fun is driving back down the hill and seeing 8 more miles range on the battery display. With gasoline prices stabilized at $4+ per gallon. It won’t be long before the common $50 per week gasoline driver drops the pump habit and turns to home plug-in.

    I was invited to a BBQ party at my workplace last week. It was on one of my days off. A coworker asked if I would attend. I said, “Yes, won’t cost any gas money”. The drive to work and back totals 31 miles. Solidly in the Volt’s sweet spot.

    http://i1101.photobucket.com/albums/g439/kawasakizx6/Voltpersonalized.jpg


  32. 32
    kdawg

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    Feb 22nd, 2013 (11:20 am)

    Walter: In fact, of you look at the two state charts George provided at the end, you’ll note that the car is actually using 50% more battery power after the series switch – from 18 amps (~6.5 kW) to 26 amps (~9.4 kW)

    I don’t see this.
    And the kW readings are negative #’s? So lower on the graph actually means more power?
    I see the HV battery power going from maybe -4 to -6, and i’m squinting to read that. It would be nice to see the graph zoomed in.
    It does seem much more consistent power flow after going into series mode. Maybe that is part of the reasoning?


  33. 33
    kdawg

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    Feb 22nd, 2013 (11:28 am)

    steve,

    “quite” a lot of typos in that post ;)

    I used to say I wouldn’t care about louder range extender, but now I hate it when my ICE turns on. I’m so used to EV driving that the rare occasions it does, I almost feel embarrassed, like i’m driving around w/a hole in my muffler. It’s not loud, probably quieter than all the cars around me, but just my reaction after typically driving with no noise or vibrations.

    On the flip side, it’s kind of a pat-yourself-on the back feeling, when you are sitting at a stop-light in cold Michigan, and everyone around you has fumes spilling out of their tailpipes, while you are in motionless/quiet/fumeless bliss :)


  34. 34
    George S. Bower

     

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    Feb 22nd, 2013 (11:47 am)

    kdawg: I don’t see this.
    And the kW readings are negative #’s? So lower on the graph actually means more power?
    I see the HV battery power going from maybe -4 to -6, and i’m squinting to read that.It would be nice to see the graph zoomed in.
    It does seem much more consistent power flow after going into series mode.Maybe that is part of the reasoning?

    negative means it is current out. Same way on MGA and MGB. It’s hard to see on the plots cuz they didn’t come thru very clear but on my good copy you can see the time averged HV Kw at -5Kw before the shift and -7 Kw after the shift. Also if you look at fig 3 you can calculate it from the currents shown (HV Volts were 333V). Calculating this way shows the power went from -6 to -8.6 Kw.

    So it does appear that series mode is less efficient.


  35. 35
    steve

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    Feb 22nd, 2013 (11:49 am)

    steve: Not necessarily, a smaller engine optimized for power generation might still be feasible.I recall someone at GM commenting that they could have gone smaller and more economical but it would have compromised how quite the car was. Considering the average noise level of cars we’re already driving now,if it sold at an appropriate price point, it would be a success.If I got better economy I might overlook not driving one of the most quite cars on the road.Heck I’m not driving anything exceptionally quite now.

    Make that quiet not quite. Duh. I miss the edit option.


  36. 36
    Zeede

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    Feb 22nd, 2013 (11:53 am)

    Awesome work, George!

    I’m guessing that if you were in Mountain Mode, then you would have PLENTY of battery buffer to deplete as you climbed a 5% hill.

    Such a brilliantly clever car.


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    pjkPA

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    Feb 22nd, 2013 (11:57 am)

    This is all long range driving …. I use the Volt as a commuter… never been above 60mph.
    In Pa the vast majority of commutes use very little high speed.. but a lot of stop and go and a lot of short 20percent grades. The Volt is perfect for this… vastly out performs any ICE. In fact hardly ever use the generator. only 6 of the 600 miles last month were generator power.


  38. 38
    George S. Bower

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    Feb 22nd, 2013 (12:13 pm)

    pjkPA:

    In Pa the vast majority of commutes use very little high speed..

    Did you know that lots of Jeff’s photos are taken in Pa? The one at the top of the article probably was. Looks nice and makes me miss “back East” as I grew up in Mass and NH.


  39. 39
    Walter

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    Feb 22nd, 2013 (12:16 pm)

    Zeede:
    Awesome work, George!

    I’m guessing that if you were in Mountain Mode, then you would have PLENTY of battery buffer to deplete as you climbed a 5% hill.

    Such a brilliantly clever car.

    Absolutely. Actually, by my quick math a Volt with the mountain mode buffer of charge at the base could manage this ascent without the engine at all, though it’s tight. The series power flow at the end shows a road load of just under 50 kW (150 amps combined with the 333 V George offered in a comment. The hill appear to take 320 seconds (100-420.) If you assume the load is constant at just under 50 kW for 5 and a third minutes, that’s 4.44 kWh. MM adds 3.5 kWh over the base ~1 kWh buffer.

    Obviously, the car wouldn’t choose to run that way. Actually, I’m very curious to see exactly how it’ll take the slope in MM. I think it’s safe to assume that it’ll hold the RPMs down for a while longer – I don’t know if it’ll come up to the 4300 in those five minutes or not.
    Walter


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    Noel Park

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    Feb 22nd, 2013 (12:19 pm)

    George S. Bower: Also I would say that it has a tendency to sway those that think a smaller range extender would be a good idea to reconsider their opinion.

    #23

    Well I never meant less horsepower. I just meant smaller in dimensions and weight. I was a booster for the 1.0L turbo 3cyl. No pun intended.


  41. 41
    Noel Park

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    Feb 22nd, 2013 (12:22 pm)

    Mark Z: BTW, Volt drivers now pass me on the freeway as I drive just above the speed limit to avoid tickets. Driving slower also helps the BEV maintain charge.

    #11

    Well I’m in the slow lane with you doing the same thing, LOL. +1

    I’ve said it before, but even if I don’t save enough on gas to justify the price of the Volt, when you add in the savings on speeding tickets, traffic school, and insurance increases, it may pencil out yet!


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    Feb 22nd, 2013 (12:24 pm)

    Walter: Absolutely. Actually, by my quick math a Volt with the mountain mode buffer of charge at the base could manage this ascent without the engine at all, though it’s tight. The series power flow at the end shows a road load of just under 50 kW (150 amps combined with the 333 V George offered in a comment. The hill appear to take 320 seconds (100-420.) If you assume the load is constant at just under 50 kW for 5 and a third minutes, that’s 4.44 kWh. MM adds 3.5 kWh over the base ~1 kWh buffer.

    Obviously, the car wouldn’t choose to run that way. Actually, I’m very curious to see exactly how it’ll take the slope in MM. I think it’s safe to assume that it’ll hold the RPMs down for a while longer – I don’t know if it’ll come up to the 4300 in those five minutes or not.
    Walter

    I’m off to Payson. I’ll run it in MM. Hopefully I won’t get held up on the hill. It’s 2 lanes but there might be a slow poke in the left lane. Actually in the summer I can get all the way to the top of this hill in regular mode without the ICE coming on and it is around 24 miles to the base.

    But now I like to run this trip in MM and save juice for in town driving.


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    Feb 22nd, 2013 (12:24 pm)

    George S. Bower: Absolutely not. It shows the brilliance of GM’s engineers to include mountain mode in the design.

    #23

    You beat me to it. +1

    Nothing negative here. Move along. Just having fun with the numbers. Thanks for your hard work.


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    Feb 22nd, 2013 (12:25 pm)

    kdawg: I think I have Andrew Farah on speed-dial, hold on…

    (j/k)

    #29

    LOL. +1


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    Feb 22nd, 2013 (12:29 pm)

    steve: Duh. I miss the edit option.

    #35

    Second the motion! +1 I don’t call myself “The King Of The Typos” for nothing, LOL.


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    Feb 22nd, 2013 (1:10 pm)

    George S. Bower,

    OK thanks, I completely missed Figure 3. Well, my only guess is that power flow is more consistent after going to series mode, and maybe that is the reason GM does it; to protect the battery from spikes/surges when the SOC is that low.


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    Feb 22nd, 2013 (1:34 pm)

    kdawg:
    George S. Bower,

    OK thanks, I completely missed Figure 3.Well, my only guess is that power flow is more consistent after going to series mode, and maybe that is the reason GM does it; to protect the battery from spikes/surges when the SOC is that low.

    I think that’s part of it. The other thing is, the car has to drive electrically during the gear shift, which it can’t do if jammed against a hard SoC limit. So mayb GM decided it was better to shift to series before it gets to the critical charge instead of carrying the more efficient mode down and trusting that it’ll be able to build some charge before it is forced to shift by some combination of speed and load.

    (They could have set it up so when it got close to a forced shift it pulled back power harder to build up breathing room. That might have been a little more efficient against the wall, but would have been much more intrusive if you hit it.)
    Walter


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    Feb 22nd, 2013 (2:00 pm)

    George S. Bower,

    George yes the battery drain was higher but the overal current use was also higher. (150A to MGB in series, 93A to MGA in power split) I wouldn’t think that the difference in efficiency is that large maybe a mild grade varation at the end caused the car draw some additional current? The elevation curve does seem slightly steeper when the car shifted to series mode. Also I believe the Volts EV motors are variable frequency? If so than strait current measurements might not directly relate to power as power factor’s would need to be taken into consideration based on the frequency.

    Also I wonder if because of gearing the maximum current MGB can generate in power split is less than MGA in series mode. MGB could be RPM limited in power split? And hence can’t generate as much electricity?


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    Feb 22nd, 2013 (2:08 pm)

    Walter: Absolutely. Actually, by my quick math a Volt with the mountain mode buffer of charge at the base could manage this ascent without the engine at all, though it’s tight. The series power flow at the end shows a road load of just under 50 kW (150 amps combined with the 333 V George offered in a comment. The hill appear to take 320 seconds (100-420.) If you assume the load is constant at just under 50 kW for 5 and a third minutes, that’s 4.44 kWh. MM adds 3.5 kWh over the base ~1 kWh buffer. Obviously, the car wouldn’t choose to run that way. Actually, I’m very curious to see exactly how it’ll take the slope in MM. I think it’s safe to assume that it’ll hold the RPMs down for a while longer – I don’t know if it’ll come up to the 4300 in those five minutes or not.Walter

    Work done lifting a body:

    W = M * F * H, where W = Work in Joules, M is Mass in kilograms, F is Force in newtons (1G = 9.81) and H is height in meters.

    Taking the Volt mass as 1818kg and the altitude change (4775-3125) as 507 meters, the work done lifting the Volt is about 9 million joules, which converts to 2.52KWh.

    That’s the pure work involved in the change in elevation and is added to energy stored as gravitational potential but does not include the energy expended overcoming air and rolling resistance at speed or George listening to ‘Flock of Seagulls’ on the sound system.


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    Feb 22nd, 2013 (2:26 pm)

    pjkPA: I use the Volt as a commuter… never been above 60mph.
    In Pa the vast majority of commutes use very little high speed.

    Is PA still 65mph? Beautiful to drive through, but that used to bother me, having to knock my cruise control down. It felt like I was going 25, even though it was probably closer to 70 LOL.

    We had a mini-snow storm in Michigan last night. I had my heater cranked this morning when I pulled onto expressway. I was figuring I would use a lot of kWh on my trip going through deep snow, but due to everyone driving 50mph or less, I ended up with more kWh left than a typical day. Amazing still how much more hi-speeds use up the battery.


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    Feb 22nd, 2013 (2:28 pm)

    Charlie H,

    I went through this math before, the last time George did a hill experiment. IIRC George assumes 15hp is lost due to friction/aerodynamics/etc.

    George correct me if i’m wrong.


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    Feb 22nd, 2013 (2:35 pm)

    Loboc:
    Nice work George! Makes waiting for my Volt even more difficult.

    Ditto.


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    Feb 22nd, 2013 (2:49 pm)

    Charlie H: Work done lifting a body:

    W = M * F * H, where W = Work in Joules, M is Mass in kilograms, F is Force in newtons (1G = 9.81) and H is height in meters.

    Taking the Volt mass as 1818kg and the altitude change (4775-3125) as 507 meters, the work done lifting the Volt is about 9 million joules, which converts to 2.52KWh.

    That’s the pure work involved in the change in elevation and is added to energy stored as gravitational potential but does not include the energy expended overcoming air and rolling resistance at speed or George listening to ‘Flock of Seagulls’ on the sound system.

    But what this analysis is missing is the power required to drive along at 66 mph for five minutes. (and you’ve assumed perfect mechanical and electrical efficiency, of course.)


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    Feb 22nd, 2013 (2:56 pm)

    Charlie H: Work done lifting a body:

    W = M * F * H, where W = Work in Joules, M is Mass in kilograms, F is Force in newtons (1G = 9.81) and H is height in meters.

    Taking the Volt mass as 1818kg and the altitude change (4775-3125) as 507 meters, the work done lifting the Volt is about 9 million joules, which converts to 2.52KWh.

    That’s the pure work involved in the change in elevation and is added to energy stored as gravitational potential but does not include the energy expended overcoming air and rolling resistance at speed or George listening to ‘Flock of Seagulls’ on the sound system.

    Oops. Saw the flock of seagulls, missed that you mentioned aero and rolling resistance already. Figure six miles at ~3.5 miles per kWh, is ~1.7 kWh. If your power for climbing is about 93% efficient, it’s consistent with my empirical approach. :)
    Walter


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    Feb 22nd, 2013 (3:04 pm)

    kdawg,

    And that 15hp, which is a power requirement, changes with George’s speed and whether or not he’s really cranking up the hair bands that day.

    The energy to climb the hill should be the energy needed to traverse that much road plus the work necessary to climb the hill.

    Has anyone ever done a careful study of Volt power requirements at different speeds? Something like two-way runs over a fairly flat course on a calm day? I was thinking that one could infer it from RE fuel economy but the figures I see are all over the place.

    PA is 65 or less everywhere. Wikipedia also says that the PA police aren’t allowed to stop you for less than 6 over. So, the real speed limit IS 70, as long as you’re otherwise behaving yourself. :)


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    Feb 22nd, 2013 (3:07 pm)

    Walter,

    And electric motors are, so far as I know, fairly efficient; the figures do seem to be in good agreement.


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    Feb 22nd, 2013 (3:14 pm)

    Charlie H,

    I haven’t seen a chart for the Volt I was satisfied with. However, it should be within 5-10% of the very comprehensive Leaf chart here:

    http://www.mynissanleaf.com/viewtopic.php?f=31&t=4295

    I suspect it may even be closer than that.
    Walter


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    Feb 22nd, 2013 (3:29 pm)

    Charlie H: Has anyone ever done a careful study of Volt power requirements at different speeds?

    Me. (this was some time ago, and I need more data. I think this is just 4 or 5 data points)

    KWvsSPEED_zps1983b1e9.jpg


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    Feb 22nd, 2013 (3:59 pm)

    kdawg:
    George S. Bower,

    OK thanks, I completely missed Figure 3.Well, my only guess is that power flow is more consistent after going to series mode, and maybe that is the reason GM does it; to protect the battery from spikes/surges when the SOC is that low.

    One other thing is. If you were a Volt engineer and you were knowing you were going to have a dead battery what mode would you want to be in? Series mode as the car can run in series at any speed as opposed to Power split.


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    Feb 22nd, 2013 (4:05 pm)

    George S. Bower,

    Sorry but at my first glance it looked like a negative article….. I guess many think it’s not. But yesterday’s article, definitely was, and that’s why I was quick to judgment.


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    Feb 22nd, 2013 (4:06 pm)

    kdawg:
    Charlie H,

    I went through this math before, the last time George did a hill experiment.IIRC George assumes 15hp is lost due to friction/aerodynamics/etc.

    George correct me if i’m wrong.

    My model was fairly close to predicting what is going on in the second PG set drawing in series, figure 3. The model has aero drag and rolling resistance at 22.75 HP and HP to climb the hill at 22.8 for a total of 66.7 HP at the tire.


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    George S. Bower

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    Feb 22nd, 2013 (4:18 pm)

    Walter,
    kdawg and all

    NEW DATA IN MOUNTAIN MODE

    OK just got back from trip to Payson in MM. It turned out pretty perfect. I ran out of juice at the bottom of the hill and was in power split just as before. Cruise set at 65 and made it all the way up without having to slow for traffic.

    From what I saw visually watching the DashDaq display, the car DID NOT SHIFT into series mode. At the end of the climb ICE RPM was 4300 RPM just as before.

    This says to me that (at least on a preliminary basis) that the shift to series was because we were getting close to PPR and the Volt wanted to be in series for PPR….. and that the response in ICE RPM was the same.

    It will take me a while to get a good set of plots because it’s a lot of data at one data point per millisecond.

    I will publish a follow up article early next week.


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    Feb 22nd, 2013 (4:27 pm)

    George S. Bower:

    I will publish a follow up article early next week.

    Looking forward to it. :) So it got to 4300 eventually, huh? It’ll be interesting to see how quickly it got there, and how much SoC it held in reserve.

    It’s undoubtedly extra work and may not be practical, but it’d be very educational if you can overlay the RPM and SoC charts from the two runs on a common graph… :)

    Thank you for helping us discover this corner of the Volt’s performance envelope. I’m learning new things here – proving again what a complex car it is, and how well GM thought it through.
    Walter


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    Feb 22nd, 2013 (4:35 pm)

    George S. Bower,

    22.75 + 22.8 doesn’t equal 66.7. What am I missing?


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    Feb 22nd, 2013 (4:39 pm)

    Charlie H:
    One thing that would make EV, PHEV and HEV operation more efficient would be topographically-aware software linked to the SOC management. As George pointed the nose of his vehicle up that hill, the nav software could have told the SOC management how much altitude would be gained. The SOC management would have realized that SOC would go very low and could have directed the ICE to begin filling the battery right away.

    To do this, nav databases would also need altitude information about every hill, which is already available from the Feds but, so far as I know, not included in .

    That’s an interesting idea, and all the tech is there to do it, provided your Nav system either has room for the full topo database or has real time connection to servers. Actually, some aircraft with TF/TA autopilots do this, kinda – they use aircraft performance models and topo maps to determine when they should start climbing for best results instead being purely reactive to the radar.

    Of course, if you’re going to do that, you should go whole hog on the Eco Nav mode – instead of setting it to normal or mountain or hold mode, the computers would be in charge of when to use the battery, too – so it can plan to use the battery on the slower roads in your trip, and (in cold weather at least) will hit the engine as soon as you hit open road if the destination is beyond electric range. Depending on the road situation, it might choose to hang on to the battery for the hill, instead of rebuilding it ahead.

    Lots of questions in optimization, but it offers the potential to keep the car smooth and nearly silent throughout the trip, as well as avoiding the inefficient high RPM fuel burn of reactive mountain mode.

    If it doesn’t become OBE due to developments in BEVs that render EREVs unnecessary, I expect to see something like this from someone in the next decade. (My crystal ball says it’ll take longer than that to get major BEV adoption, but I could be wrong – it is a crystal ball, after all.)
    Walter


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    Feb 22nd, 2013 (4:42 pm)

    kdawg,

    Interesting how the curve kinks at 75mph, which, if I understand correctly, is where the engine will lock to the driveshaft. Clearly, you don’t want to drive over 75mph unless you want to run out of charge/fuel in a hurry. But with few datapoints… maybe the curve looks kinkier than it really is.


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    Feb 22nd, 2013 (4:52 pm)

    The behaviour in power split mode is very interesting. Thanks for documenting this!

    Power split mode is a low-torque mode, that that works well at high speeds and low power demand. While driving on flat roads in power-split mode, MGA is generating power. So its sucking some of the energy out of the ICE. The extra load brings the ICE in a better fuel-efficient sweet spot, which is at a relatively high torque load. The ICE runs at 2600 rpm and MGB is near 0 RPM.

    The data shows that during hill climbing in power-split, MGA becomes a motor to helps push the ICE with an extra 30kW. Its a true parallel hybrid! Since the ICE rpm is increased from 2600 rpm to over 4000 rpm to deliver more power, MGB needs to run negative to maintain contant 66 mph speed. The data shows that MGB sucks 20kW energy out to send it up to MGA. The net effect a negative 10kW, so is the battery depletes and this cannot be sustained for long. That alone is a reason to shift to series hybrid.

    The other reason to shift to series mode is that its less efficient to let energy “go around in circles”: MGB is eating 75% of the power that MGA pushes in. That is done to enable the ICE to run in its high-rpm high-power operating point. But the conversion loss of energy going in circles is significant. I suspect that its energy-wise better to switch back to regular series hybrid under such heavy load.

    Such prolonged high-speed climbs are likely not in the standard EPA test cycle, so even if Voltec does not do this efficient it will not affect the MPG rating. From the looks of it, however, it does a great job.


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    Feb 22nd, 2013 (5:02 pm)

    RobbertPatrison:
    The behaviour in power split mode is very interesting. Thanks for documenting this!

    Power split mode is a low-torque mode, that that works well at high speeds and low power demand. While driving on flat roads in power-split mode, MGA is generating power. So its sucking some of the energy out of the ICE. The extra load brings the ICE in a better fuel-efficient sweet spot, which is at a relatively high torque load. The ICE runs at 2600 rpm and MGB is near 0 RPM.

    The data shows that during hill climbing in power-split, MGA becomes a motor to helps push the ICE with an extra 30kW. Its a true parallel hybrid! Since the ICE rpm is increased from 2600 rpm to over 4000 rpm to deliver more power, MGB needs to run negative to maintain contant 66 mph speed.The data shows that MGB sucks 20kW energy out to send it up to MGA. The net effect a negative 10kW, so is the battery depletes and this cannot be sustained for long. That alone is a reason to shift to series hybrid.

    I think I’m missing your logic here. Since the car is eating more power than the engine is producing, that’s a good reason to shift into series hybrid, where the power reaches the ground less efficiently?

    You’ll note that with the same engine rpm and presumably the same power demand/slope, the power from the battery increased by 44% when the car went from power split to series…

    In power split, the engine is pushing more power to the pavement directly than is running around the loop to hold the eCVT; in series it all has to “run the loop” – from MG A through the power electronics to MG B and back to mechanical.

    Switching to series clearly wasn’t to reduce the battery draw (except maybe as preparation for slowing down in PPR.)
    Walter


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    Feb 22nd, 2013 (5:05 pm)

    Charlie H:
    kdawg,

    Interesting how the curve kinks at 75mph, which, if I understand correctly, is where the engine will lock to the driveshaft. Clearly, you don’t want to drive over 75mph unless you want to run out of charge/fuel in a hurry. But with few datapoints… maybe the curve looks kinkier than it really is.

    Actually the car will go to Power split (your “locking to the driveshaft”) in steady state cruise as low as 35 mph.

    I do not believe there’s a sharp hook like the graph seems to suggest – just a second order function of speed from aero loading modeled with only a few data points. A smoothed squared curve through it would be much more accurate than the couple straight lines shown.
    Walter


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    Feb 22nd, 2013 (5:05 pm)

    Charlie H: But with few datapoints… maybe the curve looks kinkier than it really is.

    That.


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    Feb 22nd, 2013 (5:23 pm)

    Charlie H: the curve looks kinkier…

    The kinkier the better………. :-P


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    Feb 22nd, 2013 (5:33 pm)

    George S. Bower: My model was fairly close to predicting what is going on in the second PG set drawing in series, figure 3. The model has aero drag and rolling resistance at 22.75 HP and HP to climb the hill at 22.8 for a total of 66.7 HP at the tire.

    Oops Charlie H I meant 22.75 hp for aero and rolling resistance and 44.24 HP to climb the hillfor a total of 66.99.

    I take it back. my model is not all that accurate here because it is a sea level model. I don’t have an air density correction in it. Pressure altitude at 4800′ is about 16% lower than at sea level so my model is predicting less drain on the battery here than the data shows mostly cuz the ICE HP is less.

    Anyway, who needs a model we have real data. I have more work to do to match the model to the data.


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    Feb 22nd, 2013 (5:46 pm)

    George S. Bower: Also I would say that it has a tendency to sway those that think a smaller range extender would be a good idea to reconsider their opinion.

    Not me.

    For longer trips, I use Hold mode most of the way, and only use up the all-electric range toward the end. For people who drive long steep grades frequently, using Mountain Mode or Hold Mode is a no-brainer.

    For people that don’t drive long steep grades frequently, the worst thing that happens is you have to slow down a little, and since most long steep grades include curves, those unfamiliar with the road would tend to slow down on the curves anyway. In fact, most of the long steep grades I’ve seen have significantly lower speed limits.

    So I doubt this will ever be an issue for most people, and even if it does, it’s not a big deal.

    Bottom line: I still believe the Volt’s ICE is over-designed. A smaller, lighter range extender would make the Volt more efficient and less expensive. It would have full power in the vast majority of cases, and if you use Hold Mode or Mountain Mode properly, you’ll always have full power.


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    Feb 22nd, 2013 (6:10 pm)

    Hi George: An inspiring presentation. Well done. About your question.

    I’d guess the shift was initiated by VOLT’s altitude sensor. This might be tough to verify as speed (and perhaps temp + humidity) likely forms part of the shifting algorithm. VOLT specs its Cd at .28 . Some strongly question that. In part because its frontal area measurements come out approx 26 sq. ft. — (This is NOT reopening issues about VOLT’s specs whatsoever… Only to open up why I think the altitude sensor is operative in your data collection)

    I think a decent rule-of-thumb is power to overcome drag (for this range of Cd vs A^2) is 2:1 from 50 mph to 65 mph proportional to altitude. In any event, (#11 Mark Z) MOUNTAIN MODE really speaks a tale of how detailed engineering had to be to accomplish what GM thought was a slam-dunk in 2007.


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    Feb 22nd, 2013 (6:56 pm)

    Great analysis and write up George!


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    Feb 22nd, 2013 (6:59 pm)

    Streetlight,

    see #62 looks like the reason for the shift is that the Volt wants to be in series mode when PPR hits.

    More data on monday


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    Feb 22nd, 2013 (9:25 pm)

    George S. Bower: Did you know that lots of Jeff’s photos are taken in Pa? The one at the top of the article probably was. Looks nice and makes me miss “back East” as I grew up in Mass and NH.

    That pic could be from PA… but the road surface looks too good for a back road in PA…. and the rocks in the field make me think up state NY.

    I’m still amazed at the way my Volt climbs hills here in PA… I’m used to straining engines… one reason I loved my 84 caprice was how the 305 V8 just “ate up” hills… amazingly this little Volt weighs the same as my Caprice but “eats up ” hills with literally no effort… no noise…
    still can’t believe I’m driving a electric car…. been thinking about it since 1993 when I first read about the EV1… and knew I was going to buy one eventually after renting a EV1…
    still amazing.


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    Feb 22nd, 2013 (9:33 pm)

    I did ask the Volt adviser Ian about the clutches in the drive unit … asked if they are a wear item.
    That is …is their maintenance? he said no. but the oil (transmission fluid) in the traction unit should be changed at 98700 miles (not sure why the odd miles) … and under severe conditions 47,000 miles… that sounds like PA driving. I think he said 8 quarts .. which sounds like a lot of fluid… maybe it’s pints.


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    Feb 22nd, 2013 (10:52 pm)

    pjkPA: That pic could be from PA… but the road surface looks too good for a back road in PA…. and the rocks in the field make me think up state NY.

    It’s in Birchrunville, Chester County, PA. Very nice preserved open space. I used to climb that hill on my road bicycle on my long rides when I was doing them a few years ago. It’s steeper at spots, closer to 16 percent grade at points, and like a mile or so up up up. That point is nearing the end but the road bends to the right, and keeps ascending.


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    Feb 22nd, 2013 (11:31 pm)

    Great article George. You totally “crunched” those numbers! Awesome.

    I think you and Walter have figured out why the Volt comes out of power split. My first thought was that the car might be anticipating the need for more power. My second thought discounted that. And your MM experiment proved the second thought to be correct! It does appear that the engineers wanted the Volt to be in serial when going into PPR mode.

    On the power needed to climb the hill, Jon Lauckner said at 65 MPH (your speed) the Volt would use 30 kW (40 HP) for aero and rolling and drive train resistance on a slight uphill. That was early so the numbers might be slightly different. Assuming they’re basically OK, you’d just need to add the power to climb to this number.


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    Feb 22nd, 2013 (11:35 pm)

    Dave G: For longer trips, I use Hold mode most of the way, and only use up the all-electric range toward the end. For people who drive long steep grades frequently, using Mountain Mode or Hold Mode is a no-brainer.

    Hey Dave, I didn’t know you had gotten a Volt. Congrats! When you’re in Hold Mode will the car dig into the battery to prevent PPR mode. If it will, does the engine go to higher RPM to bring the battery back to the SOC where you set it or does it just treat the new SOC as a new setpoint?

    I think a 1.8L would be better. Not a big deal for me because I rarely use it.


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    Feb 23rd, 2013 (7:15 am)

    George S. Bower: Absolutely not. It shows the brilliance of GM’s engineers to include mountain mode in the design.

    Also I would say that it has a tendency to sway those that think a smaller range extender would be a good idea to reconsider their opinion.

    One size need not fit all. There are many, many millions in the US that live more than 200 miles from the a sustained grade that could induce a reduced power condition under reasonable speeds. There is also Hold mode which could get you farther up before power reduction. The Volt didn’t have to weigh 3700+lbs, a smaller engine would weigh less. Battery tech and other EV tech has not remained static. Newer tech will allow more efficiency and more energy storage for the same weight and power performance. Mountain Mode could be changed to be a variable set point with the current point being a floor.

    I am perfectly happy with my Volt even though I will likely never be able to use Mountain Mode. I think GM made brilliant choices at nearly every turn, including a one size fits all approach to Gen 1. The battery size, engine choice, usable charge window, control programming, battery conditioning, EVT, etc are all fantastically executed. I do believe, however, improvements can be made going forward. Volkswagen sold a lot of Beatles and Vans that were limited in power. Ultimately the consumer will have more choices of EREV architecture. GM can continue to lead that charge or resume their more usual position of the last 30 or so years and follow.


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    Feb 23rd, 2013 (7:43 am)

    steve: Not necessarily, a smaller engine optimized for power generation might still be feasible.I recall someone at GM commenting that they could have gone smaller and more economical but it would have compromised how quite the car was. Considering the average noise level of cars we’re already driving now,if it sold at an appropriate price point, it would be a success.If I got better economy I might overlook not driving one of the most quite cars on the road.Heck I’m not driving anything exceptionally quite now.

    A smaller engine could make more space for passengers, cargo, or batteries. This would be logical for gen 2.

    However, less engine power would be a bad idea. This is supported by the data posted.

    Fortunately, advances in ICE technology allow sub-1.0 Liter engines to make the necessary 75-100 hp for Volt-sized or larger EREVs.

    GSP


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    Feb 23rd, 2013 (8:08 am)

    Dave G: Not me.

    For longer trips, I use Hold mode most of the way, and only use up the all-electric range toward the end.For people who drive long steep grades frequently, using Mountain Mode or Hold Mode is a no-brainer.

    For people that don’t drive long steep grades frequently, the worst thing that happens is you have to slow down a little, and since most long steep grades include curves, those unfamiliar with the road would tend to slow down on the curves anyway.In fact, most of the long steep grades I’ve seen have significantly lower speed limits.

    So I doubt this will ever be an issue for most people, and even if it does, it’s not a big deal.

    Bottom line: I still believe the Volt’s ICE is over-designed.A smaller, lighter range extender would make the Volt more efficient and less expensive.It would have full power in the vast majority of cases, and if you use Hold Mode or Mountain Mode properly, you’ll always have full power.

    Flatlander! :-;

    GSP

    PS. I am a flatlander also, but I appreciate the Volt is made to work for everyone, whether they live in Fairbanks or Key West.


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    Feb 23rd, 2013 (8:44 am)

    DonC: When you’re in Hold Mode will the car dig into the battery to prevent PPR mode?

    Yes.

    For example, if I set hold mode with 29 miles of electric range left, then go uphill at 90 MPH, the range may dip down to 27 miles. I’ve also seen the battery level dip 1 bar below the Hold Mode set point, but that’s less common.

    I’ve never experienced Propulsion Power Reduced mode.

    DonC: If it will, does the engine go to higher RPM to bring the battery back to the SOC where you set it or does it just treat the new SOC as a new setpoint?

    The range extender recharges the battery level back to the Hold Mode set point, but not right away, it seems to take a few minutes to work its way back.

    DonC: Hey Dave, I didn’t know you had gotten a Volt. Congrats!

    Yeah. We waited for better selection and better deals. The 2013 model also has quite a few improvements.

    Also, we actually prefer cloth seats over leather. For 2011/2012, cloth seats were only available with the white center stack, which we both found distracting. The 2013 Pebble cloth interior option solved this issue.

    I was also hoping the 2013 model would be FlexFuel as GM originally promised, but that’s life. You can’t always get what you want.


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    Feb 23rd, 2013 (9:07 am)

    Koz: The Volt didn’t have to weigh 3700+lbs, a smaller engine would weigh less.

    Exactly, +1

    Koz: There is also Hold mode which could get you farther up before power reduction.

    Actually, I believe Hold Mode can prevent power reduction completely. For example, if you set Hold Mode with at least 25 miles of range left, I don’t think there’s any road in the world that will cause Propulsion Power Reduced mode. Steep grades don’t last forever, and most include curves that limit your max speed.

    I’m also very skeptical that people will experience reduced power if Mountain Mode is used properly. The typical comment is something like “I forgot to set Mountain Mode before hand, so I was forced to slow down a little.”

    Koz: Mountain Mode could be changed to be a variable set point with the current point being a floor.

    How would this be different than Hold Mode?


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    Feb 23rd, 2013 (9:18 am)

    GSP: However, less engine power would be a bad idea. This is supported by the data posted.

    The data posted shows:
    1) A driver that typically drives long steep grades at fairly high speeds.
    2) This driver typically uses Mountain Mode to solve any potential issues.
    3) Even when this driver purposely tries to cause Propulsion Power Reduced mode, it never occurs.

    To me, this suggests that the Volt’s current range extender is over-designed.


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    Feb 23rd, 2013 (9:39 am)

    pjkPA: I’m still amazed at the way my Volt climbs hills here in PA… I’m used to straining engines… one reason I loved my 84 caprice was how the 305 V8 just “ate up” hills… amazingly this little Volt weighs the same as my Caprice but “eats up ” hills with literally no effort… no noise…

    Right. I’ve found the same.

    Your comment also brings up an excellent point: Many other cars have to reduce speed up long steep mountain roads, either because of strain on a small engine, or because the radiator starts to over-heat near the top. So this isn’t unusual.

    The Volt is normally much better than average on mountain roads, and if you use Mountain Mode, it’s always works great. The worst thing that can happen is that you forget to set Mountain Mode, and you have to slow down a little, like many other gas engine cars.


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    Feb 23rd, 2013 (10:26 am)

    Dave G: The data posted shows:
    1) A driver that typically drives long steep grades at fairly high speeds.
    2) This driver typically uses Mountain Mode to solve any potential issues.
    3) Even when this driver purposely tries to cause Propulsion Power Reduced mode, it never occurs.

    To me, this suggests that the Volt’s current range extender is over-designed.

    I’m pretty sure that mountain climbing has nothing to do with the sizing of the Volt’s engine. I believe the main requirement for power is the sustained 101 mph speed limiter drive.

    For the first generation, there were other big factors… The 1.4L is a simple, reliable, off the shelf engine that they could drop directly into the car – a big consideration considering the miracles they were committed to performing in such a short period. The 1.4L is basically the same as the Cruze engine without the Turbo, which likely gave them a leg up on the EPA certification process, and certainly simplified the logistics and reduced the engine cost.

    Honestly, I’m expecting the next generation engine to be larger, actually. I think we’ll see an engine based on the 2.0 DI block with dedicated Atkinson cycle and very high compression ratios – giving similar power output with substantially improved efficiency.
    Walter


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    Feb 23rd, 2013 (12:02 pm)

    Once again kudos to George for a great analysis, and kudo to the posters for many intelligent comments. It’s going to take me more than a few days to digest the information presented. This is a wonderful example of why I love this forum, please keep up the good work.


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    Feb 23rd, 2013 (12:22 pm)

    GSP: A smaller engine could make more space for passengers, cargo, or batteries. This would be logical for gen 2.
    However, less engine power would be a bad idea. This is supported by the data posted.
    Fortunately, advances in ICE technology allow sub-1.0 Liter engines to make the necessary 75-100 hp for Volt-sized or larger EREVs.


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    Feb 23rd, 2013 (12:24 pm)

    GSP: A smaller engine could make more space for passengers, cargo, or batteries. This would be logical for gen 2.
    However, less engine power would be a bad idea. This is supported by the data posted.
    Fortunately, advances in ICE technology allow sub-1.0 Liter engines to make the necessary 75-100 hp for Volt-sized or larger EREVs.

    Walter: Honestly, I’m expecting the next generation engine to be larger, actually. I think we’ll see an engine based on the 2.0 DI block with dedicated Atkinson cycle and very high compression ratios – giving similar power output with substantially improved efficiency.

    I don’t really care how big the engine is, the main concern for me is that the car performs the same in RE mode as it does in EV mode. I don’t want to have to limp around when I’m on gas.


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    Feb 23rd, 2013 (12:31 pm)

    Charlie H: One thing that would make EV, PHEV and HEV operation more efficient would be topographically-aware navigation software linked to the SOC management.

    Yes, very true. Though the hard part is designing software to anticipate the intentions of human beings who have the infinite possibilities availabe to them of the open road.

    Mike: An OEM calibrator explained to me that incorporating the NAV would make it part of the “emissions system” since it could control engine operation. That brings baggage they prefer to avoid, specifically with warranty requirements.
    That said, I could swear I read that BMW did something similar in one of their hybrids.

    Good point Mike thanks for including that.

    Mike: Thanks for the taking the time to present this great data George.

    Yes thank you very much George!

    Dave G: Yeah. We waited for better selection and better deals. The 2013 model also has quite a few improvements.
    Also, we actually prefer cloth seats over leather. For 2011/2012, cloth seats were only available with the white center stack, which we both found distracting. The 2013 Pebble cloth interior option solved this issue.
    I was also hoping the 2013 model would be FlexFuel as GM originally promised, but that’s life. You can’t always get what you want.

    Wait, what whoa! I thought you were “out” when the Volt price was annouinced! I did the same thing and got a 2013 White diamond, the incentives are too hard to pass up.


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    Feb 23rd, 2013 (1:09 pm)

    Walter: If it doesn’t become OBE due to developments in BEVs that render EREVs unnecessary, I expect to see something like this from someone in the next decade. (My crystal ball says it’ll take longer than that to get major BEV adoption, but I could be wrong – it is a crystal ball, after all.)
    Walter

    #65

    Sounds about right to me. +1


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    Feb 23rd, 2013 (1:32 pm)

    jeffhre: Wait, what whoa! I thought you were “out” when the Volt price was annouinced!

    I waited until the price came down to less than $30K after the federal tax credit.

    We don’t get any state tax credits or other incentives here.


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    Feb 23rd, 2013 (1:36 pm)

    Walter: I’m pretty sure that mountain climbing has nothing to do with the sizing of the Volt’s engine. I believe the main requirement for power is the sustained 101 mph speed limiter drive.

    Not quite following you here. Please clarify.


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    Feb 23rd, 2013 (2:16 pm)

    Dave G: Not quite following you here.Please clarify.

    Not sure how much of this you know, so forgive me if I’m repeating a lot of the obvious.

    During the preliminary design phase of a vehicle (car, airplane, space craft, etc.) you start by defining constraints from what you expect it to do. These might come from customer requests, from legal requirements, from marketing research, or from experience with past vehicles.

    These constraints determine the the design choices you make as the design matures. Sometimes, a particularly difficult constraint ends up shaping the entire design, leaving a vehicle that does one thing very well, at the cost of doing everything else poorly. Others end up well rounded, with few standout abilities.

    In a normal car, you’d have three or four constraints driving your power needs – acceleration, hill climbing ability, top speed, possibly towing. On the other hand, fuel economy and cost targets lead to the smallest, lowest power engine that meets the above. The Volt is different, however…

    The battery and drive motors handle acceleration, so it isn’t a sizing constraint for the ICE.

    Hill climbing is less clear, but it’s still a mix – as mountain mode demonstrates, there’s room to trade sustained power against buffer size.

    Sustained top speed OTOH, means sustained power. I believe GM picked the 100 mph requirement early, to address that “not a real car” perception. Combined with the aero and rolling performance, this requires the ~55 kW output to the road.

    So the point I was making is that I think they picked the size/power of engine that they right after committing to production based on the top speed target – and that they added mountain mode after determining from either modeling or testing that in some high speed hill climbing situations they didn’t have enough power to sustain the high speeds – which were likely assessed as being a rare enough operating condition that it made more sense to add the mode in software than to get a larger engine which would reduce fuel economy the rest of the time and even electric economy (due to increased weight.)

    As it is, the engine operates in the optimal range at 70-75 on the flat, hits the bottom of the optimal range at WOT at 1400 between 60 and 65 (below which, rather than throttling the engine, it cycles the engine on and off,) and at peak output delivers enough power for 100 mph or most hills at 65-70. Combined with being a simple off the shelf install for their limited development cycle, it was clearly a wise choice.

    For second generation, with more time and (presumably) more budget/flexibility, I’m expecting we’ll see a DI Atkinson design of similar power output. (The constraints that led to the sizing decisions likely aren’t changed.)

    Make sense?
    Walter


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    Feb 23rd, 2013 (2:31 pm)

    Editing function restored

    I’m told you all can now edit your posts again. You will have 60 minutes to rework a comment.


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    Feb 23rd, 2013 (3:33 pm)

    Jeff Cobb:
    Editing function restored

    I’m told you all can now edit your posts again. You will have 60 minutes to rework a comment.

    #98

    Best news I’ve heard today. +1


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    Feb 23rd, 2013 (3:52 pm)

    Walter:

    Honestly, I’m expecting the next generation engine to be larger, actually.I think we’ll see an engine based on the 2.0 DI block with dedicated Atkinson cycle and very high compression ratios – giving similar power output with substantially improved efficiency.
    Walter

    That would be my bet also.
    I think we could easily see a 10% increase in ER mode MPG.
    I already ran the analysis but did not publish a article on it.


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    Feb 23rd, 2013 (6:52 pm)

    Walter: (The constraints that led to the sizing decisions likely aren’t changed.)
    Make sense?

    The constraints are, as you say, somewhat arbitrary, and based on typical perceptions of electric cars in 2007. Tesla has done a lot to change these perceptions, so these constraints are probably be outdated.

    Walter: and at peak output delivers enough power for 100 mph…

    I feel safe in saying that most people don’t need to drive constantly at 100 MPH. This particular design criterion is set too high. Many people drive up to 100 MPH in short bursts, perhaps while passing, but driving for hours at 100 MPH is not a necessary design constraint.

    It would be better to size the range extender for an average speed of 80 MPH, and let the battery buffer handle short bursts up to 100 MPH.

    Long steep grades would be handled by Mountain Mode or Hold Mode, or in the worst case, by simply slowing down a little. Since long steep grades are uncommon for most drivers, this is not a big deal.

    I believe the real issue is this: Most people still equate ICE size with max power. With an EREV, this simply isn’t true. The ICE only supplies average power.


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    Feb 23rd, 2013 (7:15 pm)

    Walter,

    Except that sales may say we need more performance, like from direct connecting a 2.0 or + liter turbo. Oh, the beauty of the Voltec transmission, with the ability to direct connect a performance ICE. With little effect on economy, when driven normally.


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    Feb 23rd, 2013 (9:19 pm)

    Dave G

    How would this be different than Hold Mode?

    The only significant difference, and it is particularly important for this situation, that I know is that Mountain Mode builds charge to a set point. If you remember to set hold mode soon enough or you just get used to traveling in hold mode on long trips, it won’t matter. They could also just combine the two and let you adjust the hold mode SOC even if that is above the current SOC. IMO, this is how GM should have implemented it out of the gate.


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    Feb 24th, 2013 (4:42 am)

    Jeff Cobb,

    Now all we need is the link to activate it (Monday’s soon enough ;-) ).


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    Feb 24th, 2013 (6:48 am)

    Koz: They could also just combine the two and let you adjust the hold mode SOC even if that is above the current SOC.

    Yes.

    Perhaps the best solution would be a simple dial that allows you to set how many miles until your next charge. This way, the car could figure out the best way to manage the battery level while maintaining ample power. The default would be something like “short trip”, and would be like Normal Mode. If the remaining all-electric range is low when you set the dial, the range extender would slowly recharge the battery to a level that provides ample power for climbing hills, just like Mountain Mode does today. The main difference would be that toward the end of the trip, Mountain Mode would automatically disengage, so that all of the available battery energy is used.

    Some people have suggested using the GPS for this, but there are many problems:
    1) When you reach your GPS destination, you may not be able to plug in.
    2) Many people don’t use the GPS for common destinations.
    3) You can’t change the GPS destination while driving.
    4) Many people don’t buy the GPS option, myself included.

    By the way, after state sales tax, our third party GPS device cost $1378 less than the Volt GPS option, includes lifetime traffic and map updates, and allows us to set our destination while driving. It’s also really nice having a dedicated third LCD for traffic and map info, allowing the center stack LCD to show music and climate info without interruption.

    We mounted our GPS on the front left corner of the Instrument Panel Storage cover. In this location, it doesn’t obstruct the view of the road at all, and the plastic hump that covers the center stack LCD makes a perfect hand rest for configuring the GPS. Also, the 12v power outlet in the Instrument Panel Storage compartment hides the GPS cord and FM traffic dongle really well.


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    Feb 24th, 2013 (8:08 am)

    kdawg: I don’t really care how big the engine is, the main concern for me is that the car performs the same in RE mode as it does in EV mode. I don’t want to have to limp around when I’m on gas.

    I agree.

    I wouldn’t consider myself a particularly efficient driver. I like to drive fast, and have plenty of power for passing. I’ve gotten the Volt up to 96 MPH while passing uphill, without really trying. I’m sure there are many others posting here that have also gotten the Volt near or at the 100 MPH limit.

    But it’s also important not to over-design the thing.

    How many people here drive the Volt constantly at 100 MPH for hours? None.

    So why was the Volt designed to do this?

    As Walter says, perhaps to alleviate any misconceptions about electric cars, or perhaps because they happened to already have a 1.4L engine which is also used in regular gas engine cars, probably a little of both.

    But moving forward, it seems to me that a less powerful range extender would provide just as much power to the wheels 99.99% of the time, and you could make that 100% by using Mountain Mode or Hold Mode properly.


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    Feb 24th, 2013 (8:46 am)

    Dave G: But moving forward, it seems to me that a less powerful range extender would provide just as much power to the wheels 99.99% of the time, and you could make that 100% by using Mountain Mode or Hold Mode properly.

    Isn’t every step in that direction making the Volt more like the P-word car? NVH every time you step on the accelerator.


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    Feb 24th, 2013 (9:03 am)

    Eco_Turbo: Isn’t every step in that direction making the Volt more like the P-word car? NVH every time you step on the accelerator.

    Moving forward, I expect we’ll see many new types of EV range extenders.

    For example, the Sterling engine uses constant external combustion (ECE), so there are no popping explosions inside the pistons, practically eliminating noise, vibration, and harshness (NVH), while also reducing cost, improving efficiency, and reducing emissions.

    And if they can use nano-tech to get the price of direct ethanol fuel cells down, the range extender would have no moving parts, so NVH would be zero.

    The point is that disconnecting the engine from the wheels removes a major design constraint. This is a game changer, allowing all sorts of designs that aren’t viable for traditional gas engine cars. Car makers have yet to take advantage of this.


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    Feb 24th, 2013 (12:37 pm)

    A few random thoughts:

    The Power Split mode is very interesting since it is essentially backwards from the way I thought it should be operating, i,e, traction motor does the mechanical work, ICE and MGA generates the power for the traction motor. Instead the ICE and MGA is doing the work and the traction motor is along for the ride. Rather than shut the traction motor off entirely, it’s fields we’re energized and it acts as a generator, but it also places a load on the system. I guess the trade off in power split is worth it.

    I’m also guessing the shift occurred because the power output from the power split configuration was no longer sufficient to maintain constant velocity. The ICE and MGA were both operating at max operating levels. The switch to series mode also allowed a lower gear ratio, but this required the traction motor to spin at high RPMs to supply adequate power. I believe this is why the current drawn from the battery is higher in series mode, that is, the series configuration can handle the higher power requirements, the power split could not.

    It seems to me that this shift would not have had to occur if the ICE could provide more power in the power split mode. I agree with you that a dedicated extended range ICE makes a lot of sense. A 2L running an Atkinson cycle, high compression, DI, and operated with its throttle wide open sounds like just the ticket to get the MPGs up closer to the Prius, but I don’t think physics will allow the MPG to reach the Prius because the additional weight the Volt had to carry, this of course does not apply to Ford as they have somehow overcome the weight penalties in their plug-ins and still advertise Prius like MPG numbers.

    Your point about what configuration to be in when you are about to go into Reduced Power is well taken. I would think going into series mode in anticipation of this occurring makes sense as this is the configuration the Volt will have to be in if this were to occur.

    Once again, thanks for a great analysis that adds to our understanding of the Volt.


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    Feb 24th, 2013 (2:18 pm)

    Eco_Turbo: Isn’t every step in that direction making the Volt more like the P-word car?

    By the way, conceptually, it’s the other way around. A parallel hybrid get’s more of it’s power from the gas engine and less from the electric motor. An EREVs gets more power from the electric motor, and less from the gas engine. A pure BEV gets all of its power from the electric motor, and there is no gas engine.

    In other words, a smaller gas engine would make the design more EV and less hybrid.


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    Feb 24th, 2013 (3:00 pm)

    Larry4pyro: A 2L running an Atkinson cycle, high compression, DI, and operated with its throttle wide open sounds like just the ticket to get the MPGs up closer to the Prius, but I don’t think physics will allow the MPG to reach the Prius because the additional weight the Volt had to carry…

    Yes, Atkinson cycle is a step in the right direction, but I doubt a 2L is necessary. Remember that the data in the article shows reduced power mode never occurred, even when the driver tried to force it, so the existing 1.4 is more than adequate. A 2L would make the Volt even heavier.

    By the way, here’s a question: What is physically different for an Atkinson cycle engine? Is it just the cam shaft? Could the existing 1.4 engine be converted to Atkinson cycle?

    Larry4pyro: this of course does not apply to Ford as they have somehow overcome the weight penalties in their plug-ins and still advertise Prius like MPG numbers.

    Not sure if you’ve heard, but Consumer Reports has questioned C-Max and Fusion Hybrid MPG numbers, and the EPA is investigating.
    http://www.detroitnews.com/article/20130114/AUTO04/301140402
    ” Consumer Reports said the C-Max hybrid’s fuel efficiency fell 10 miles per gallon short in testing — it got 37 mpg overall, with 35 mpg for city driving and 38 mpg highway. The Fusion Hybrid, certified for the same 47 mpg, got 39 mpg in testing overall, with 35 mpg city and 41 mpg highway.”


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    Feb 24th, 2013 (4:12 pm)

    Eco_Turbo: Isn’t every step in that direction making the Volt more like the P-word car? NVH every time you step on the accelerator.

    Not necessarily. The burden could be bourn by the battery, which it is now for a lot of the power. The electric motors are responsible for nearly all acceleration as it is. The battery augments the power from the motor. Only sustained high loads require high output from engine and that is at speed when engine noise is not as much of an issue. The driving quality advantages to the Volt are during EV mode and swifter acceleration as it is, IMO. A lower weight range extender increases range and improves acceleration. It could also lower cost and free up much needed space. A 3200lb Volt would do nicely with 12kwh usable, 10 more KW from the motor, and a max 35kw genset. Good acceleration 40 to 70mph, @45 AER EPA, 45mpg CS mode, and a little noisier going up sustained grades at high speeds.


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    Feb 24th, 2013 (6:40 pm)

    Koz: Not necessarily. The burden could be bourn by the battery, which it is now already used for a lot of the power. The electric motors are responsible for nearly all acceleration as it is. The battery augments the power from the motor. Only sustained high loads require high output from engine and that is at speed when engine noise is not as much of an issue. The driving quality advantages to the Volt are during EV mode and swifter acceleration as it is, IMO. A lower weight range extender increases range and improves acceleration. It could also lower cost and free up much needed space. A 3200lb Volt would do nicely with 12kwh usable, 10 more KW from the motor, and a max 35kw genset. Good acceleration 40 to 70mph, @45 AER EPA, 45mpg CS mode, and a little noisier going up sustained grades at high speeds.