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Full-battery downhill engine start is a pain!

Discussion in 'Toyota Prius Plug-in' started by chuckp, Mar 23, 2012.

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  1. chuckp

    chuckp Junior Member

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    I have a frequent commute which is 11.4 miles and can be nicely done with only the battery. However, I live on top of a hill, and as I descend the hill on the full battery before I get to the bottom the engine starts! This does not happen if I drive around the block a couple of times to waste some charge, or use the emergency brake to descend the hill!! Of course once the engine starts it runs for several minutes before it shuts off. I find this behavior very strange. Why start the ICE because the battery got too full? What's the matter with the brake shoes? Of course I can stop the engine and start the car again to force it off, but that seems very silly. I've made many multi-mile runs on level ground without this strange behavior, so it took me quite a while to figure out the reason for the engine start. There's no way I know of to charge "not quite" all the way, so I see no reasonable solution to this strangeness.

    Chuck
  2. Tracksyde

    Tracksyde Member

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    I've run into the same situation. However, I have avoided it by doing the following:

    1. Accelerate briskly through my neighborhood just to use up a little more electricity than normal (for me, there's only 2 chances to do this, and I'm only accelerating briskly for maybe 20-40 feet at a time.. this may not be doing much, but using any bit of extra electricity can help here)

    2. Coast down the hill and apply heavier braking, limiting the amount of regneration and increasing the amount of brake pad use.

    I've measured the battery's state of charge (SoC) when the ICE was starting and when it reaches 84%, the ICE will turn on to prevent the battery from going beyond its limit. In my case, I'd leave my house with 85.1% SoC, drive down the street, down a slight hill to a Stop sign. Then accelerate (briskly) from a right hand turn. But now, my SoC is around 83.1% to 82.9% or so. The road then goes downhill for about 1/4 mile to the next stop sign. If I'm not "careful" with the regen, it will regen up to 84%. This morning I was able to keep the ICE from starting by following the method I mentioned above.

    The ICE starts to prevent the battery from going beyond what Toyota has deemed "safe" for the battery pack. As I mentioned above, a full charge is 85.1%. The ICE starts at 84%.
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  3. cproaudio

    cproaudio Speedlock Overrider

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    Start with a depleted battery at the top of the hill. Once you started driving down hill, you can look at the MFD to determine how many Wh the descent can generate. Once you've determine that, you can do some calculations to determine at how many % SOC you should stop the charger. If the descent can generate 2kw of electricity, that's 2kw less you have to recharge at home.
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  4. ryogajyc

    ryogajyc Active Member

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    Have you tried selecting B gear?
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  5. Tracksyde

    Tracksyde Member

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    I'll try B tomorrow and log the data and compare with the data from the above method. If B works, that would be much easier :D
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  6. kammssss

    kammssss Member

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    Put it on N. I do it all the time.
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  7. qbee42

    qbee42 My other car is a boat

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    Are you sure that the ICE is actually starting? It sounds to me like it is doing engine braking, where the ICE is spun by the electric motor to dissipate excess charge.

    With a full battery you have no room for regenerative braking. When descending the hill, regenerative braking creates charge, so the Prius spins the ICE to dissipate this charge. This does not waste fuel.

    Tom
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  8. mmstuart

    mmstuart New Member

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    Same here I live on a hill and have noticed the problem happens more frequently. It did not happen the fist couple days I owned the car. And yes it is ICE that comes on. I first go step down a step grade and in .5 to .7 miles the ICE kicks in and stays on 2 to 4 minutes even after after going down for 1 mile and then starting a climbing up a step grade for 30 seconds with a gentle EV foot. I agree it is a real pain and it drives down the overall MPG vs staying in EV more until it is depleted.

    If I drive 1 mile up a hill from 700ft to 900 ft elevation and then regen down the other side to sea level over 5 miles the ICE never kicks in and even driving up to 62 MPH in stop and go traffic I can get up to 17.4 miles in EV mode.
  9. andyprius

    andyprius Senior Member

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    IMHO: You should not worry about it, it is probably just the engine spinning which uses the excess regen charge. Toyota has very ingeniously designed at least three computer systems all designed to work in cooperation Hence: the HSD concept. Let the computers do thier thing and you only have to enjoy the PIP. :cheer2:
  10. OilFreedom

    OilFreedom New Member

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    Does the PiP charging schedule allow you to set the max SOC you want? For example, if you live on the top of a hill (as we do too), then you could set it to charge to just 80% instead of 85.1%.

    The Leaf has two options to automatically end the charging: 80% and 100%. When I use 100%, I have to drive a few miles before getting any regen to speak of. Since there is no engine for engine braking, the brake pads get a lot more use when I hit the brakes. With 80%, I get full regen right away and spare the brake pads. Unless I need the extra range, it makes more sense to just give it an 80% charge so I get the regen benefits right away.
  11. SageBrush

    SageBrush Senior Member

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    Perhaps you could put the charger on a timer so that you start your morning with a bit of room in the battery for the downhill regen
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  12. andyprius

    andyprius Senior Member

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    Regeneration is good, you cannot over-regenerate! The engine shows as running on screen, in reality the engine is only spinning. Don't sweat it!
  13. SageBrush

    SageBrush Senior Member

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    By the way, battery capacity changes with temperature. People outside of So CA and Hawaii can expect to fiddle with this at least twice a year if they also start their mornings going down a long hill.
  14. SageBrush

    SageBrush Senior Member

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    Yep, no petrol wasted on the way down; but he paid to get up that hill and he wants his money (and energy) back! :)
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  15. andyprius

    andyprius Senior Member

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    Too late! he spent his money wisely, by going up the hill with a Pip. :D
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  16. Rebound

    Rebound Senior Member

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    In this situation -- Downhill with a fully charged battery -- B gear is much better than N. With N, the friction brakes do all of the stopping. That's not good; they can wear and, on a big enough hill, they can overheat. Using B will slow the car by spinning the engine, which is a well- known method used in manual and automatic transmission cars and trucks. Although the engine spins, no fuel squirts in, so no gas is consumed. The friction brakes are still used, but they get an assist from the engine braking. Got it? Drive safe. :)
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  17. usbseawolf2000

    usbseawolf2000 HSD PhD

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    I think B will do the thing as when you hit the 84% full.

    N gear suggestion is a good one. Perhaps it stops the regen and only use the friction pads.
  18. usbseawolf2000

    usbseawolf2000 HSD PhD

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    I think they want to keep the MPG at 999.99. When the ICE spin in B gear, it drags the MPG down for some reason. Perhaps it uses some gas....
  19. Allannde

    Allannde Just a Senior

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    The issue for me, here, is that IF the ICE is firing up, it needs to run long enough to get warm enough to evaporate the water and mildly acidic combustion byproducts which, over time, increase ICE deterioration. I never shut down a cold engine and my cars seem to last longer than others. But that uses more fuel. I suspect that the long term savings in repair cost and the lack of down time inconvenience are worth it.

    By the way, I use "B" to prevent the added regeneration of using the brake pedal on a downhill.

    I have not found a way in the PiP owner's manual to set for less than a full charge as one can in a Leaf.

    I will learn more in a few days when my PiP arrives.
  20. bisco

    bisco cookie crumbler

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    you could set the charge start time later so it isn't fully charged when you unplug to leave. start with 15 minutes and experiment until you have it down to a science.
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