Any Volt owner switching over to Prius PHV?

Discussion in 'Gen 1 Prius Plug-in 2012-2015' started by usbseawolf2000, Feb 4, 2012.

  1. H2OSkier

    H2OSkier Member

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    This is very interesting. I had the exact same feeling when I looked at the Volt at the LA car show. Not very easy getting in and out. I'm not what I consider a huge guy, 6' 185 lbs.
     
  2. sxotty

    sxotty Member

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    That is a 5.2C rate. 83 kW from Volt would be the same.
     
  3. ItsNotAboutTheMoney

    ItsNotAboutTheMoney EditProfOptInfoCustomUser Title

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    I think he means something like the following:
    I leave my house and join the Interstate one mile away. I then drive 3 miles up a hill (100ft/mi elevation change).* If I do that thoughtlessly like a "normal" driver my car's engine will turn on cold to assist the car to get up a 3 mile hill at 65mph.

    For comparison, in a Prius liftback the engine has had a mile of warm up at lower loads before having to work hard to pull the car up the hill at high speed.

    I think what he missed is that the grid charge in the pack can be used gradually to ramp up the load on the engine.

    * That is my fastest route to work. Actually, I hardly ever take that route and even if I do I go up the hill at 50mph precisely to avoid working the engine hard.
     
  4. Jeff N

    Jeff N The answer is 0042

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    I haven't seen any hard data along the lines of the recently posted cold start thread that measure what is happening during a cold start under load. Typically (as in the recent thread) a regular Prius cold start happens within seconds of "starting" the car. The engine enters a warmup protocol while the owner is backing out of the garage or pulling into low speed local traffic. As far as I can tell, there is normally low load on the engine during the first minute or so of the warmup and as much of the typically low power requirements are taken from the battery as possible.

    The PiP does something similar most of the time. About 1-2 miles before the EV range runs out the car will start the gas engine and run it through a low load warmup protocol. However, if there is an aggressive acceleration at city traffic speed or a somewhat less aggressive acceleration at highway speed or while going uphill then the cold engine will spontaneously need to be started and driven under significant load (a normal low-load warmup only generates 1.25-2.5 kW for the first 55 seconds according to the recently posted charts). I suspect this significant load will not result in the usual 50 mpg efficiency and super clean emissions that are typical of a warm Prius powertrain.

    I don't have carefully measured data to back that assumption up but I'm suspicious about the claim that "blending" and "balancing" power under heavy torque demand between the electric motor and gas engine while nominally in EV mode is somehow better than staying all electric if you have a larger battery pack that makes that possible (Volt, etc.).

    I'm curious if once the gas engine is started it will complete its warmup protocol even if it is no longer needed. In other words, you need extra power to accelerate for 5 seconds but will the engine continue to run after that until it is finished with its warmup routine? I suspect it will.

    Regardless of the battery SOC, once the gas engine has been started, will the PiP be much more likely to restart the engine even while nominally driving in EV mode similar to how the PiP operates after the engine has been warmed up under low-load near the last portion of EV range?

    The reason for this would be to keep the warmed-up engine warm for emission control reasons. At least one of the major Prius PHEV conversions would use the battery to supply about 50% of the blended power to drive the car normally but had a California emissions mode where it drained the battery at only a 25% contribution rate. The increased blending of gas engine power effectively kept that engine and catalytic converter hotter and significantly lowered engine emissions.

    How will the PiP behave? I don't know but I'm interested in finding out. John or others may have had enough time behind the wheel with the PiP prototype to know the answers for it but I suspect nobody yet knows the answers definitively for the 2012 production PiP.
     
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  5. Jeff N

    Jeff N The answer is 0042

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    Okay, I tested this yesterday and you are correct.

    I started my 2004 Prius, which had been in the garage overnight at 45-50F, and immediately backed out and drove at typical 30 mph speeds through local streets for 1.5 miles and then drove on the highway at 65-70 mph.

    For the first mile the consumption display showed about 17-20 mpg average. At around 2.5 miles at showed 30 mpg average. Just after 4 miles it showed 35 mpg.

    These numbers are likely skewed due to spending part of the time stopped at intersections as the engine was running it's warm up cycle. On the other hand, much of the power to drive the car for the first minute may have come from draining the battery which was then replenished. It's hard to make too many judgements without much more carefully measured data via the OBD II port and I'm not equipped or motivated enough at the moment to gather it.
     
  6. austingreen

    austingreen Senior Member

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    You need to do some USBMath (tm) to get this right:D It takes an assumption of a low conversion of say 13kwh/gallon of gas, and other weird assumptions that there is a secret way having low max power optimizes things.

    But joking aside, in engineering terms the question is not if it makes it worse, but how much worse. This like most questions comes with the answer - it depends. If you end up with 95mpge using blended gas and electric, you will end up using very little gas, but YMMV. In the case that it is much worse, well that means that much higher power was called upon, which would burn through that battery pack rather fast. Cold starts cause extra pollution, but the prius is an exceedingly low emission (in cali arb speak super duper low emission), and if we didn't have screwed up tests during the drive would pollute even less than a prius. All in all its not a bad trade off. The worse really comes down to having fewer electric miles, not the little bit of gas blended during these miles. The worse may also come into NVH and driving feel, but until someone can test drive them, we won't know. Toyota may have improved the drivability of the phv.

    Toyota engineers are probably still working on the software, and can do changes even after the cars are shipped. 1 minute of warm up on a prius is not going to make or break you.

    Its good to have choices. Some will find the seats more comfortable, some will want the extra range or lower cost, etc. I would think no one would trade a volt for a phv, but the real idea is these plug ins compete more with more conventional cars. If someone buys a volt or prius phv or ford energi its a good thing. 1 size does not fit all.
     
  7. john1701a

    john1701a Prius Guru

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    I have a ton of experience with this, 3 generations of Prius in fact.

    My hill climbing and hard acceleration into traffic is just 30 seconds from my house, far too close for warmup to complete. You can very clearly feel the electric motor taking the brunt of the load to allow the gas engine to ease into it.... especially in the dead of winter.

    That was a major design aspect which drew me into Prius ownership in the first place. December 2000 was both the second snowiest and second coldest December in Minnesota history. It was a heck of a way to dive into the hybrid world.


    Warmup is so fast, it will. Reaching 103F (the shutoff threshold) in my 2010 occurs while I'm waiting at the stoplight 2 blocks from my house. PHV warms up even faster.


    I doubt it. That's not the way my 2010 works now. EV is solid as long as the coolant temp is at least 157F.

    Unless draw exceeds the kWh threshold, the engine should stay off.
    .
     
  8. SageBrush

    SageBrush Senior Member

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    Electric motors have efficiency curves, too. A perfect blend would optimize the ICE *and* the motor.

    Moreover, as battery discharge rates increase waste heat increases faster than the increase in discharge. If I understand battery chemistry correctly, this is true over and above battery ambient temperature increase effects.
     
  9. sxotty

    sxotty Member

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    What is the maximum efficiency of the ICE? What is the efficiency of the electric motor at maximum allowable revs? I don't think this is really comparable at all since ICEs are pretty miserable when it comes to efficiency.
     
  10. john1701a

    john1701a Prius Guru

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    Overall operation was 37% for Prius originally.

    The 2010 model bumped it to 38%.

    Toyota is currently experimenting with two different concepts for the next generation. One is 42.4% and the other 43.7%

    Pretty sweet, eh?
    .
     
  11. usbseawolf2000

    usbseawolf2000 HSD PhD

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    With less than a month until deliveries, the excitement is mounting. Will Prius PHV blend? How will the EV and HV mode differ? What is the pure EV range? Is 38kW battery power enough for city driving lower than 62 mph?

    How will it be better than Volt? Is using a little more gas a better strategy to optimize both fuels?

    Will the size, price and cargo capability overcome gasoline anxiety? We will find out more clear answers soon!
     
  12. sxotty

    sxotty Member

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    No.

    It is nice for an ICE, but miserable compared to an electric motor.
     
  13. usbseawolf2000

    usbseawolf2000 HSD PhD

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    The efficiency to convert chemical to mechanical energy is quite low. Power plant efficiency from fossil fuel (coal, natural gas and oil) to electricity is worse -- DOE use 32.8%. Electricity from solar is even less. Nuclear is 97% efficient!

    It is easy to realize vehicle efficiency because EPA label makes it easy. It is just as important to know the efficiency of the fuel production you'll be driving with.
     
  14. telmo744

    telmo744 HSD fanatic

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    I didn't follow. No or Yes, is it sweet or not, after all?
     
  15. usbseawolf2000

    usbseawolf2000 HSD PhD

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    My calculation is nothing new. It is known as well to wheel (WTW) analysis. Google it and you'll find a lot of papers for your reading. Basically, you include fuel production efficiency and vehicle efficiency to get the total energy efficiency from the well to the wheels. EPA label only cover pump (or plug) to wheels and leave out well to pump.

    Electricity equivalent to a gallon of gas:

    33.7 kWh x 0.39 (39% fuel production) x 0.85 (vehicle efficiency) = 11.17 kWh equivalent WTW.

    Similarly, a gallon for a gallon of gas:

    33.7 kWh (gallon equivalent) x 0.84 (84% fuel production) x 0.38 (vehicle efficiency) = 10.76 kWh WTW.

    The chart below from Toyota sums it up nicely visually.

    [​IMG]

    I think the gas engine will stay on for about 42 seconds. That's when the warm up cycle would complete. While the gas engine (and Cat Conv) are warming up, it can recharge the battery back to the initial (prior to switching to HV mode) state of charge. Hybrid mode is charge sustained.

    After that, EV mode can resume. The result is low power easy EV miles. 200 Wh/mi should be quite realistic.

    Leaf and Volt won't have the luxury of the hybrid mode to utilize. So, the battery will have to cover maximum power hard EV miles that increases the average watt-hour per mile consumption.

    38 kW power requirement for various cycles is quite frequent. It is easier to look at the 40kW mark. Also notice the frequency between the 40kW and the maximum.

    [​IMG]
     
  16. drinnovation

    drinnovation EREV for EVER!

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    You are using old DOE numbers. (32.9 is 1995 data reported in 1999 I think and used in teh 2000 PFF formula).

    A more recent report
    http://www.iea.org/papers/2008/En_Efficiency_Indicators.pdf
    concludes
    Between 1990 and 2005, the average efficiencies of coal-fired
    plants have risen in most countries, with increases of about half a percentage point in OECD countries and of two percentage points in non-OECD countries. US coal plants now average 36% efficiency.

    Natural gas plants are even more efficient. Between 1990 and 2005, the average efficiencies of natural gas-fired plants have risen significantly in many countries. As a result, the average efficiency in OECD countries has increased by almost eight percentage points, while non-OECD
    countries have seen a two percentage points rise. US NG-based plants in 2000-2005 averaged 43% efficiency. So the Prius may someday get there.


    The above report shows US overall fossil-fuel based efficiency for 2001-2005 was 37%. (Japan in that report was 43% for just fossil fuel..)

    Since fossil-fules accounts for 71% of US electricity generation, that's not the whole story. We generate 39% of electricity with minimal fossil fuel and you cannot just ignore it.

    If one including Nuclear and renewable (Hydro and wind with small amounts of others) at say 97%, then the overall electric fuel generation efficiency is about 54% with respect to fossil fuel usage.
     
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  17. wjtracy

    wjtracy Senior Member

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    ...you guys and gals buying Prius PiP and Volt are early adopters, or you have compelling quality of life/cost benefits such as access to HOV lanes and big rebates. Congrats! Paving the way for the rest of us. But I would not expect defections in the ranks, if anything more Volts if CA gives Volt HOV access. A little questionable to hear cost of gasoline as a justification in this price range, as preumably could buy a 40 mpg gaso car for $15K or less.
     
  18. wjtracy

    wjtracy Senior Member

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    Good data thank you I want to study it. The bottom line is at national average elec fuel use, Leaf and Prius HEV are about equal CO2 emissions = approx 50 MPG = approx 50 MPG fossil fuel equivs. Ignor EPA 100 MPGe for the moment, because that number is not intended to reflect fossil fuel burning equivalents. I personally see Volt as approx 37 MPG and 37 MPG fossil fuel equivalents EV mode, but your numbers could be better if you have a clean elec source, or much worse say in Pittsburgh on grid with high coal% and winter MPGe losses.
     
  19. SageBrush

    SageBrush Senior Member

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    A footnote to these figures says
    Hmm. This explanation is informative:
     
  20. austingreen

    austingreen Senior Member

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    I would not call 38% miserable, it is getting close to diesel efficiency.

    But this is peak efficiency at the shaft. There are two problems with using this number for blended mode.

    1) The cold engine efficiency is much lower. When the engine kicks on to blend it will either go through a warm up phase or kick high speed. This means a much lower efficiency.

    2) When high power is called upon at low speed, a high percentage of the power must be generated at mg1 then sent to mg2. This means it will take the full efficiency hit of mg2 to the wheels.

    The best case for prius engine to wheels efficiency is warmed up in its 220g/kwh at speeds where the transmission is efficient.
     
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