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after reaching speed, what does taking foot off accelerator do?

Discussion in 'Gen 3 Prius Main Forum' started by priustexasbob, Feb 12, 2011.

  1. priustexasbob

    priustexasbob Member

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    I've seen a several of "how to get best mileage" videos and each one always shows them taking their foot off the accelerator pedal for an instant after reaching cruising speed, then applying slight pressure.

    I know this is a component of P&G, but why do that instead of just reducing pedal pressure to achieve the same ECO indicator result? what does removing the foot and reapplying accelerator pedal pressure do that just reducing pedal pressure doesn't do?
     
  2. Prius O Matic

    Prius O Matic Junior Member

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    One thing I've noted (in my extensive 3 weeks of experience :rolleyes:) is that it feels as if the CVT changes to a higher ratio, almost as if it "shifted" to Overdrive. As if it could 'shift'.

    The trick seems to be maintaining speed while keeping it functioning in this mode.
     
  3. qbee42

    qbee42 My other car is a boat

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    The Prius control system works hard to guess how the car will be driven. Backing off just a bit on the accelerator tells the control system not to accelerate. Coming off the accelerator tricks it into thinking that you are going to slow down. It's just a method of spoofing the ECU into doing what you want.

    Tom
     
  4. Mendel Leisk

    Mendel Leisk Senior Member

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    That release the gas and gently re-apply is one of the suggestions in the Owners Manual (page 35, introduction to the Hybrid System Indicator), for achieving better mileage.

    If you've got the display set up to show your fuel economy (Hybrid System Indicator, page 192), warmed up engine, and good state of charge in the hybrid battery, watch what happens:

    Lift your foot off the gas. The HSI bar drops to nothing, down to the left end. Coincidentally the Instantaneous Fuel Consumption display (item 3, page 181) should climb to infinite (US) or drop to zero (metric).

    Now gently re-apply gas, being careful to keep the HSI bar to the left of the centre dividing line. Your IFC display should continue to show no fuel being consumed.

    In other words, the engine shut off (when you lifted off the gas), and continues to be off: your motivation is solely from the Hybrid Battery and electric motor.

    One caveat: this can eat up the Hybrid Battery's state of charge fairly quickly. Try to keep the HSI bar as much to the left as possible, to minimize consumption.

    I've got one stretch where I can go well over a kilometer in this state. The flip side is it's consuming the state of charge quickly, and ultimately putting more wear-and-tear on the battery. So I would take it when it comes, but don't go looking for it too aggresively.
     
  5. Much More Better

    Much More Better Active Member

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    Sometimes I ease up on the accelerator until the bar is just into the HSI zone, and at some point in the gas reduction, the engine shuts off, the same as it would if I had lifted my foot right off and re-applied.

    I P&G with only a small triangle of a bar inside the HSI zone, and therefore, I am decelerating. I try not to drive at a constant speed with battery only because of increased battery usage, and I don't believe is it efficient to have to recharge by running the ICE.
     
  6. dtuite

    dtuite Silverback

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    What Mendel said.

    And if you're on a downhill, you may be able to coast further than a click, while using the motor-generator simply to maintain a constant speed. And, expanding that concept, if there are little hills, you may be able to coast the up sides without losing too much velocity and quickly pick up speed on the downsides with a little boost from the battery without causing the internal combustion engine to start.

    That's an aspect of pulse-and-glide that is closer to normal speed control than the more obssessive oscillaton between 42 and 18 mph of the hardshell flatland hypermilers. You won't match their results, but you may create less road rage. There's a hypermiling spectrum. pick a range where you're comfortable.
     
  7. donaldhall

    donaldhall New Member

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    If your were going to 70mph and then maintain 70 I seen no reason to lift off the gas pedel. I believe the lift is only for around town type driving.
     
  8. ksstathead

    ksstathead Active Member

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    Actually, for times with traffic so you need a more constant speed, pulse UP and glide down. Or just DWL (allow speed to bleed down by avoiding added throttle on the ups, slowly regain with same throttle on the downs).

    When all alone, glide up and pulse down (huge speed range inappropriate to sharing roads and getting there quicker)..

    Hypermilers that interfere with traffic are not following the cleanmpg guidelines where hypermiling was coined.
     
  9. ksstathead

    ksstathead Active Member

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    Agreed. Generally. Wind resistance makes warp stealth more of a "downhills and exits" strategy for me. It can work, but is not as practical/natural as P&G below 45 mph (41 mph gen2).
     
  10. F8L

    F8L Protecting Habitat & AG Lands

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    This technique is not limited to the Prius. Conventional automatic transmissions can be hastened to drop into a higher gear when this technique is employed.

    Additionally, when observing both the scangauge and the MFD, I have noticed the two often differ in there readings when using this technique. I wonder if this is one the reasons the MDF and hand calculated MPG differ.