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Cruise control deceleration increases regen?

Discussion in 'Gen 3 Prius Technical Discussion' started by neergh, May 18, 2010.

  1. neergh

    neergh New Member

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    I recently noticed that when driving my gen 3 T-Spirit (UK spec) with cruise control engaged, that when after setting a desired speed and I hold the lever in '-SET' position the deceleration is more pronounced than expected i.e. more than just releasing the gas (accelerator) pedal. The engine is not running and the brake is not depressed. The eco meter displays increased regen while I hold the level in '-SET'. The engine does not appear the be running as it would in 'B' mode.

    When the road permits, I now set cruise and hold the lever down in -SET when I want decelerate a bit more without pressing the brake or going into 'B'.

    Has anyone else noticed this with the cruise control or am I mistaken?
     
    #1 neergh, May 18, 2010
  2. Paradox

    Paradox Prius Enthusiast / Moderator
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    Without looking at the CC stalk, doesn't holding the - down just reduce your set speed on the CC? So it basically makes the car decrease speed down to a new set speed. All you're doing is kind of coasting or decelerating down to a new preset cc set speed...
     
    #2 Paradox, May 18, 2010
  3. fuzzy1

    fuzzy1 Senior Member

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    The 2010 CC does use active means to slow the car. Where previous models just went into a free coast-down mode, the 2010 increases regen braking, and spins up the engine for compression braking when the HV battery is full.

    I, and several other PC regulars, use this to maintain constant speed on some downhill slopes where the car wants to coast faster. I don't use CC enough to know whether it is also applied in OP's situation, setting the SET speed down on level ground, but strongly suspect that it is.
     
    #3 fuzzy1, May 19, 2010
  4. neergh

    neergh New Member

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    Thanks Fuzzy1

    When on country roads I set the cruise control for 30-40 mph and accelerate past it to say for example 60 mph and when I want to slow down the I can use the extra regen.

    Will this reduce to use of the friction brakes and increase the amount of regen charging for the battery? For example when I leave a motorway (freeway) on the way to work I have to normally decelerate from 70 mph to 0 mph in 500 yards. By setting the cruise control to 30 mph and allowing the increased deceleration I get another 30 W/hr symbol on the 1 min display over conventional braking.
     
    #4 neergh, May 19, 2010
  5. Flaninacupboard

    Flaninacupboard Senior Member

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    You're probably right that the cruise control deceleration won't use -any- friction braking, wheras braking yourself at those speeds it would be a blend.

    Does it get you slightly more regen than braking yourself? possibly. is it a safe thing to do? no. if someone following you is not paying attention and you slow considerably with your cruise method, and your brake lights don't illuminate..... could be nasty!

    Another possiblity is that you're just braking too hard yourself, to max your regen you don't want to overfill the charge bar on the HSI. set your HUD to show the HSI as well, and then you can watch it while braking.
     
    #5 Flaninacupboard, May 19, 2010
  6. Philosophe

    Philosophe 2010 Prius owner

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    In ref to your first question: I don't think so, no.

    You may simply use the brake pedal and a look at the HSI to keep it inside the CHG part and you will achieve the same maximum regeneration. Be aware that at high speed a very slight pressure on the brakes will quickly push it to the regeneration limit.

    Using the cruise control in a freeway exit to slow the car down will not light up the brakes light: you may be rear-ended... or not having your foot ready on the brake pedal may increase your braking distance and you could then rear-end someone... not good.
     
    #6 Philosophe, May 19, 2010
  7. Philosophe

    Philosophe 2010 Prius owner

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    Duplicate.
     
    #7 Philosophe, May 19, 2010
  8. fuzzy1

    fuzzy1 Senior Member

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    The brake pedal already has access to the full regen capacity of the car. The CC has no additional tools to do any better. And the appropriate CC setting would be a moving target, very difficult to adjust at the necessary rate.

    Stick with the brake pedal in the case.
     
    #8 fuzzy1, May 19, 2010
  9. neergh

    neergh New Member

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    The CC is better in some circumstances IMHO. You can use B but that keeps the engine turning. If you press the brakes at higher speeds is not always desirable to get more regen with the brake lights turning on. The CC method is is a gradual slowing down when I think you want to slow down a bit quicker then just coasting without feathering the brake.

    All I do is set the CC to say 40 mph and then drive normally to higher speeds when I need to slow down gradually I just resume the CC and brake if necessary for more retardation. I don't use it in traffic only been experimenting with the CC so far.

    If you have a manual car (stick shift) which most cars this side of the pond are, you can obviously use a lower gear to increase the retardation of the vehicle. I think the Prius is good in this department as there are options on ways to slow down depending on the road conditions.
     
    #9 neergh, May 20, 2010
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