Best strategy for a long cruise down hill

Discussion in 'Gen 4 Prius Main Forum' started by mudworm, Sep 7, 2018.

  1. kevinwhite

    kevinwhite Active Member

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    I'm not sure what you mean.

    When there is no car to follow the car will go to the set maximum speed (adjusted with the stalk).

    Along i5 the speed of the traffic when there was any was reasonable - if I wanted to overtake a truck or slow car I just changed to the fast lane, the car would then accelerate to the set speed until I went back to the other lanes.

    kevin
     
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  2. kevinwhite

    kevinwhite Active Member

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    I usually set the following distance to the largest setting - that's far enough that I don't think it is perceived as "tailgating".

    Agreed the radar loses sight of the followed car on sharp bends, most of I5 is not too bad - you can disable the following mode if you wish to revert to constant speed.

    kevin
     
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  3. alanclarkeau

    alanclarkeau Senior Member

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    He later said that he's got something like 176 bends and a bit tighter than I envisioned - so ignore my suggestion.

    The scenario I was thinking was more open sweepers, but some corners tightened up, so following another car, my PRIUS just followed along.
     
  4. mudworm

    mudworm Member

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  5. alanclarkeau

    alanclarkeau Senior Member

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    Woops - sorry.

    As I said:
    upload_2018-9-10_11-32-48.png
     
  6. mudworm

    mudworm Member

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    No worries. You had no good way to tell. What's obvious to me is not always obvious to others.
     
    #26 mudworm, Sep 9, 2018
    Last edited: Sep 10, 2018
  7. Rangerdavid

    Rangerdavid Senior Member

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    I have a steep descent to work and a reverse steep climb to get home. Usually on the way down, I use "B". My battery is as full as it gets when I get to work, but Prius has so many protections to prevent overcharging, I don't worry. Even if I don't use "B", when full, the engine will increase revs to prevent overcharging. I just use "B" so I don't over use the brakes.
     
  8. Smaug1

    Smaug1 Member

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    There's no danger of overcharging. This is something Toyota would have designed into the charge circuitry.

    Once the battery is charged and if you need to touch the brakes, you're better off using 'B' for engine braking. It can slow you down surprisingly quickly and is adaptive, unlike on a manual trans car. You won't use ANY gas while engine braking. Just a bit of electricity, which is easy enough to re-generate.
     
  9. Smaug1

    Smaug1 Member

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    The engine RPM increasing is a byproduct of what the car is really doing: reducing the gear ratio. (engine braking)
     
  10. tucatz

    tucatz Active Member

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    Hey mudworm, don’t keep us in suspense - which mountain pass in the Bay Area are you talking about? I use B mode going down highway 24 and any of the hills from skyline blvd down into Oakland. I rarely touch the brakes, end up with a full battery charge, and usually average 52 mpg for the trip (up and down the mountain). I did this religiously on my 2010 prius and sold it at 90K miles with 70% of the brake pads left.
     
  11. mudworm

    mudworm Member

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    Is your cat that curious? It's not a pass. It's just Hwy 84 / La Honda Rd that goes over Rte 35 / Skyline Blvd. I didn't know Skyline Blvd goes all the way into Oakland.
     
  12. tucatz

    tucatz Active Member

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    I used cycle the Old La Honda Road - Skyline - Portola Valley loop when I lived in Palo Alto.

    Oakland has its very own Skyline Blvd.
     
  13. A440SPS

    A440SPS Junior Member

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    It seems sensible to use "B" mode when going down a moderately steep hill, say with a 30 mph speed limit.

    But "B" mode revs the engine fairly high. Once the battery is fully charged, is it better to shift to "D", and lightly ride the brake to slow down with regeneration rather than friction, and not wear the engine at all?
     
  14. sam spade 2

    sam spade 2 Senior Member

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    NO. "Once the battery is fully charged", the regen energy goes into spinning the engine and not to the battery........regardless of the position of the "shifter".
     
  15. fuzzy1

    fuzzy1 Senior Member

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    But it doesn't redline. In fact, at least in my Liftback, it doesn't rev significantly higher than it needs when climbing the hill. It is just more noticeable.

    When the battery is fully charged, there is no more regeneration possible. So you must slow down with either friction brakes, or engine braking. Or both.

    For short hills, it is your choice of brake pad wear vs engine wear. For long hills that might overheat the brakes, the engine compression braking becomes essential.
     
  16. alanclarkeau

    alanclarkeau Senior Member

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    Isn't that what "B" is for - I think I read that the ICE will spin to almost 5000rpm max in "B" - which is short of redline - and I suspect with no fuel being used. Brakes cost money to replace.
     
  17. A440SPS

    A440SPS Junior Member

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    That's helpful, thanks. I didn't realize that the regeneration braking relies on the electrical load of the battery.

    Still, if I have to choose between wearing out brake pads, and wearing out piston rings, wouldn't I choose brake pads? Surely engine braking causes wear on many engine components.

    --Cy--
     
  18. alanclarkeau

    alanclarkeau Senior Member

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    TOYOTA's instruction:

    upload_2018-12-31_8-7-49.png

    The engine will almost certainly last the life of your car - don't forget that it has a rest when in EV Mode so it's only running 75-80% of the distance travelling.

    Brakes will wear quickly if used on downhill stretches - and could even overheat if the stretch is too long, as they're designed to be used in conjunction with Regeneration braking and "B" mode.
     
  19. fuzzy1

    fuzzy1 Senior Member

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    For short hills, your choice, depending on your own vehicle experience. As some people point out, brake pads are cheap. As others point out, the engine normally lasts the life of the car, or at least doesn't often fail from this wear mechanism.

    I drive on numerous long hills, so safety dictates not overheating the brakes.

    Pike's Peak Road descent, mandatory brake check at Glen Cove, where a pickup truck a bit behind me and smelling to high heaven was ordered into the 30 minute cooling off zone (sorry for less-than-idea Google view): Pikes_Peak_Glen_Cove_brake_check.JPG
     
    #39 fuzzy1, Dec 30, 2018
    Last edited: Dec 30, 2018
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  20. Mendel Leisk

    Mendel Leisk Sunday driver DIY’r

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    Would engine braking be a time of high vacuum in the cylinders? This tends to pull oil up most effectively, lubing the highest zones of the cylinder walls that the piston rings contact.

    Again, I would reserve B for long downhill stretches, where the hybrid battery is full to the top bar and still a lot of downhill ahead.
     
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