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Prius PHV: Optimization strategy with lessons learned from the prototypes

Discussion in 'Gen 1 Prius Plug-in 2012-2015' started by usbseawolf2000, Mar 18, 2012.

  1. usbseawolf2000

    usbseawolf2000 HSD PhD

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    Following an advanced press drive of the new 2012 Toyota Prius C, just-auto spoke with Satoshi Ogiso, the lead engineer for the four models in the newly expanded 2012 Prius range: Liftback, Prius V (known as Prius+ in Europe and Prius Alpha in Asia), Prius C (called Aqua in Japan), and the upcoming Prius Plug-In Hybrid.

    Ogiso is one of the few engineers who have been with the Prius program since its inception as the G-21 project in the early 1990s. He spoke about Toyota’s development of its new plug-in hybrid model, its views of series hybrid technology, and how he sees customer demand evolving for electric vehicles.

    Q: You ran a fleet of several hundred prototype Prius Plug-In Hybrids for two years before putting the 2012 model into production. What changes did you make between the prototypes and the production car?

    A: We changed the battery pack, also the powertrain programming, and we improved the electric range.

    First, the battery pack is smaller (4.4 kilowatt-hours rather than 5.2 kWh), and we use different lithium-ion cells, from Sanyo. The new pack contains 56 rectangular large-format lithium cells, in four modules of 14 cells. Each cell has 21.5 Amp-hour capacity, operating at 3.7 Volts. But the usable portion of the pack’s energy capacity has remained almost the same, despite the smaller capacity.

    Second, we made the power electronics more efficient, and we improved the control programs to maximize the efficiency of the entire powertrain, as well as the accelerator behavior. And we were able to reduce the weight of the car by roughly 70 kg (150 lbs), mostly due to the smaller battery.

    Taking all of those changes together, we have expanded the all-electric range by about 10 percent. [Depending on temperature and driving style, it ranges from 9 to 15 miles.]

    Q: What data did you gather about typical usage patterns for the prototype plug-in fleet?

    A: We learned that no single usage exists! [laughs] People used them in many different ways, for short and long trips, many times a day or just once.

    Q: How did you choose the pack size, since you get only 9 to 15 miles of electric range—versus 25 to 40 in, say, a Chevrolet Volt?

    A: For the plug-in Prius, it was very important to optimize efficiency for all usages, and to retain the fuel efficiency when operating in hybrid mode. A higher electric range means more weight from a heavier battery, which hurts fuel economy, as well as less space inside. So, we try to make the most efficient vehicle in all operating modes.

    Q: In the prototype Prius Plug-In, once the battery pack had exhausted its electric range, the pack would not recharge beyond the 1.2 kWh of a standard Prius. Has that changed?

    A: Yes. You can now recharge the pack beyond 1.2 kWh, if conditions permit. It would be technically possible to use regenerative braking to recharge the pack completely to 4.4 kWh, if you had dozens of miles of downhill travel. But, of course, such conditions do not usually exist in real driving.

    Q: Other manufacturers have chosen a different architecture, the range-extended electric car, in which the engine is used only to generate electricity and not to power the wheels, once the pack is depleted. Is that an avenue Toyota is pursuing?

    A: It is very important to make sure we have the lowest fuel consumption when using the engine to power the car. It would be foolish for our image of efficiency to use that energy to make electric power rather than to drive the wheels.

    Even if much more efficient engines come along in the future, designed to power generators, their output should be used to power the wheels. Because our Hybrid Synergy Drive has two motor-generators, we can choose easily and freely how we blend power from the engine and the motor, from moment to moment. That is how we maximize efficiency under all circumstances.

    Source
     
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  2. John in LB

    John in LB Life is good

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    EXCELLENT QUESTIONS/ANSWERS! Really spot on as to logic.
     
  3. giora

    giora Senior Member

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    The beauty of HSD: it gives an extra degree of freedom.
     
  4. Paradox

    Paradox Prius Enthusiast / Moderator
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    I posted in another thread that yesterday coming back to NYC from Lancaster PA I was able to recharge the pack from a .8 EV mile range to 10.4 miles of EV range. So recharging the pack through regenerative braking is definitely do-able. :)
     
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  5. 2sk21

    2sk21 Member

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    There are definitely some long grades in the region that might allow such charging. Was this long stretch on I-80 or I78? Even on the Palisades Parkway north of NY, there are some long grades that require me to switch to B on the shifter.
     
  6. giora

    giora Senior Member

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    With Prius HEV, the justification of using B mode is remote.
    With the Prius PHV it is almost never...
     
  7. Paradox

    Paradox Prius Enthusiast / Moderator
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    I78 and also some on 222 which I use to cut across to I30. When you're on 222 speeds are about 45mph but there are lights in towns. If I saw the light changing ahead I'd let off the gas, hit the ev mode to go into ev and then brake lightly if necessary. Once the light changes, hit the button to go back into HV mode and you gain around .2-.3 ev mile range. Over the whole trip it really stacks up to recharge the whole pack.
     
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  8. drinnovation

    drinnovation EREV for EVER!

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    Interesting, though it seems complex. The normal prius does regen and gains ev range on such a stop. Is this really just the same amount but more obvious because of the display? Wouldn't the natural stop/start of the Prius really save the battery just as much? I guess I could see the manual switching to EV more efficient as it shuts the engine down just a bit sooner, but that should not really result in more EV, just less gas used. Maybe the added mass of the PiP allows a bit more regen?
     
  9. HillCountryEVer

    HillCountryEVer New Member

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    That is very cool! I also believe that others are finding that they can achieve some amount of increased EV range when driving at speeds above 65. Both approaches are significant and very exciting!
     
  10. Paradox

    Paradox Prius Enthusiast / Moderator
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    I've talked about this in my other thread and it's not really complex at all. If you run in HV mode and go down a hill the recharge given to the battery thru regen is used up to help mazimize mpg's. Basically, the car keeps the EV distance constant at what it was when you switched from ev to hv. Now, IF you do what I described above it allows you to acculate and stack the regen gains so when you arrive at your destination you could have a fully charged or near fully charged battery, depending on driving conditions. Coming home yesterday I was able to go from a .8 ev mile range to a 10.4 ev mile range through regen on downhill descents or from having to stop at traffic lights from near highway speeds going through small towns.
     
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  11. pineprius

    pineprius 15th Hole #4

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    Picking up our PIP in VA and driving back to NC 120 miles, noticed similar response. Partially charged due to 15 miles of test drive, both EV and HV mode, left dealer with 3.7 miles of EV charge, but by 80 miles and about 400 feet of elevation change (downhill, which is not very much) was showing 13.2 miles of EV, without any effort in HV mode. For 3 days in somewhat rural town, 3 charges and zero ICE time. This is performing exactly how the car was marketed. Even wife is smiling now that around town it's all EV. :spy:
     
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  12. fjpod

    fjpod Member

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    Sounds good, but wouldn't this reduce the mpg's during highway driving as the extra power could be sent to the wheels? Wheel power is better than battery power, no?
     
  13. 9G-man

    9G-man Senior Member

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    Gosh I admire those Toyota engineers. I don't think anyone realized last year, that the desire for selectable EV power usage in the Prius PHV, would result in the added benefit of selectable regen/powersplit charging.
    But it makes total sense, and works the way I thought it might.
     
  14. 9G-man

    9G-man Senior Member

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    An ordinary car engine is working far outside it's efficiency range cruising down the Hwy. The regular Prius can take advantage of its Atkinson engine and HSD, at the right RPM to eliminate some of this inefficiency,ei "Super Hwy Mode. But there was still a remainder of excess power that it sent to the battery as a charge/deplete cycle, constantly at hwy speeds. You can see it happening on the Energy Screen. Well it appears the PHV can use that remainder of extra power to just charge, without a lose in engine efficiency at that speed.
    When EV mode it selected at Hwy speeds?
     
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  15. Trollbait

    Trollbait It's a D&D thing

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    I was thinking the same. Paradox's description, with manual switching between modes, made it sound as if energy recaptured during the coast could be saved for later EV use and kept from maximizing mpgs in HV mode. Which implied and either/or situation.

    Pineprius's account shows this isn't true, and a manual switching isn't necessary. A non-PHV Prius could easily max out its SOC during a long downgrade, or winter months with more ICE use. A PHV has a larger battery to save that excess generation, and better options in reusing it. Since the limits on EV mode in the liftback generally only leave blasting max AC has a way of bleeding of the charge in most situations.
     
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  16. Paradox

    Paradox Prius Enthusiast / Moderator
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    If I didn't switch to EV mode during descents the charge built up was used rather quickly to help assist the engine. It was so brief I didn't see a huge benefit in it aiding MPGs. A bigger benefit, for me, was having a 10+ mile range in EV once i got up there or got back home to driving surface streets. It'll take alot of experimentation to see what works best for people I guess.
     
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  17. usbseawolf2000

    usbseawolf2000 HSD PhD

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    So, switching to EV mode removes the target state of charge (TSOC). HSD would not deplete the charge unitil it reaches the TSOC.

    After you bump up the EV range, you switch back to HV mode and a new TSOC would be set. HSD will maintain that unless you remove it by switching to EV mode.

    This adds flexibility as both power sources interact with one another.
     
  18. ksstathead

    ksstathead Active Member

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    So long as one is able to use the accumulated EV range before the next charge opportunity. That is, you wouldn't want to store regen that the gasoline produced and then have no room for wall charging.
     
  19. 9G-man

    9G-man Senior Member

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    I think there might be some confusion.

    Paradox is pointing out that Regen energy can charge the battery for increased EV range, if in EV mode during the Regen.

    Pineprius and others are noticing that HSD operation, during highway travel, is charging the battery with increased EV range. Regardless of mode.

    Two different observations.
     
  20. andi1111

    andi1111 Member

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    I don' think your approach is wise. Your end result is the same if you switched from EV to HV sooner, before you run out of EV range. Furthemore, you're harming your battery. The system is set up for short charging bursts from regen and slow charging from the wall. What you're doing is chargin your battery from zero to full with many rapid chargings, which is very harmfull to the battery. Even Nissan recommend not to do quick charging to often and that is only aprox. 2C charging. What you're doing is 9C charging from zero to full with occasional pauses. Do you think it won't have any effect on the battery pack?
    I would really recommend you stop using this approach if you want your battery to last.
    If ou neee EV driving at the end, switch to HV sooner.