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Pulse & glide at "high" speeds

Discussion in 'Gen 3 Prius Fuel Economy' started by pakitt, Sep 8, 2010.

  1. pakitt

    pakitt Senior Member

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    correct me if I'm wrong - Pulse & Glide is not really possible at speeds higher than, say 120-130km/h (74-80mph). I have noticed on my last trip that if you want to keep 130km/h average and you pulse up to 140km/h and glide down to 120km/h, when "gliding" the engine never shuts down, and the glide period is very short.
    When pulsing back to 140km/h it takes a "long" time and the instant fuel consumption is "high" (e.g. 6-7L/100km) while when "gliding" you are actually at 2-3L/100km, which means on average you are at about 5L/100km, which is what I would get in any case if keeping speed constant with the CC at 130km/h.

    Up to what speeds does Pulse & Glide really work and beyond which speeds (the question is more for those who can actually drive at those speeds - e.g. most of the US drivers legally cannot go over 80mph) it simply does not help and the fuel consumption is then independent from driving technique and rather relies on overall efficiency of the car when at constant speed driving (with CC on to ease the foot)?
     
    #1 pakitt, Sep 8, 2010
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  2. ksstathead

    ksstathead Active Member

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    Technically, p&g only goes up to 45 mph (gen3) or 41 mph (gen2). We use p&g to refer to a glide with the engine not spinning.

    Above those speeds, the term we use is warp stealth, in which the engine spins to protect MG1 from overspeed, but no fuel is consumed. Wind resistance at the higher speeds is so severe than warp stealth only works on exits, traffic slowups, downhills.

    So, at higher speeds, you can use cruise control, or you can do driving with load in which you try to maintain a fixed instantaneous mpg by letting speed slowly decrease on the climbs, making it back on the descents.
     
    #2 ksstathead, Sep 8, 2010
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  3. pakitt

    pakitt Senior Member

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    A-ha! I knew it! - and I was trying to improve FE doing P&G at around 130km/h and seeing the battery would never be used...:rolleyes:

    Actually at those speeds, the engine does all the work, except when you are really pushing it and gets help from MG2; and sometimes even in those cases, the engine is in the most efficient area compared to the MG2, that it manages to charge the battery, give current to the MG2 and push the car as well.

    In steady load (i.e. flat road - very difficult to get in Europe, or at least where I live), there is a ping/pong of electricity going to and fro the battery which is kept steady at 6 bars (if I remember correctly). It goes up to 8 if you go down a very long hill/descent. The only way to discharge it is to hit a traffic jam where, as you said, you can do P&G.

    P&Stealth, is for me quite difficult to achieve, as I see that as soon as you press the gas a tiny bit too much or hit an even minor climb, the engine goes in "happy mode" (as I call it) by which the ICE drives the wheels "directly" (MG2 and the ICE spin at the same speed, I believe) and no current goes to MG2 and MG1 charges the battery.
    This is what I mean.
    As soon as I see instantaneous fuel consumption higher than 0L/100km, it means that I am out of Stealth, right? or is "happy mode" the Stealth mode?

    Good - now I can happily use CC not feeling guilty of using the "best" driving technique - there is simply nothing I can do...:)

    As for using hills ("driving with load") loosing speed and then regaining it once going down, hills here are *so* long on highways/freeways it is practically impossible to do it. More possible is with countryside roads (when then you can also P&G).
     
    #3 pakitt, Sep 8, 2010
  4. priustexasbob

    priustexasbob Member

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    ok, i'm going to show my Prius newbie-ness. what is pulse and glide?
     
    #4 priustexasbob, Sep 8, 2010
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  5. ksstathead

    ksstathead Active Member

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    OP: I concur. stealth no good at high speeds. DWL no good on long climbs.

    bob: The idea is to use the ICE for brief periods of thrust (near the PWR section of the HSI on gen3), then back **almost** off the throttle so the HSI bar disappears completely (no arrows on gen2). This latter step is the glide and mimics neutral in a normal car. No battery use or regen in either pulse or glide, in theory. This is repeated within a speed band (say 41 to 35 in a 40 zone).

    Gliding is also crucial to good town mpg even beyond p&g, as in gliding toward red lights.
     
    #5 ksstathead, Sep 8, 2010
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  6. paulh

    paulh Junior Member

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    When you glide do you just take your foot off the gas pedal or do you throw the Prius into neutral???
     
    #6 paulh, Sep 9, 2010
  7. ksstathead

    ksstathead Active Member

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    Neither.

    I keep slight throttle pressure so that the regen braking associated with no throttle (designed to simulate engine braking in a normal automatic tranny car) is canceled out as indicated by the absence of any bar in the HSI display.

    There are times when some use neutral gliding, and you can try that if you need to know what 0G gliding feels like, but you should first and foremost learn to glide using the throttle, as that is one of the great features of the Prius. You get the benefits of engine off gliding using nothing but your go-pedal. Normal cars need a manual transmission, an injector kill switch (or can use the key), shifts to and from neutral, a bump start. All we have to do is let up on (but not off of) the throttle.

    I only come off the throttle when I need to slow faster than a neutral glide.

    Press up the tires a bit and Prius will glide till the cows come home.
     
    #7 ksstathead, Sep 9, 2010
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  8. priustexasbob

    priustexasbob Member

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    thanks for enlightening me on this. I've been kinda doing this on long slowdowns to a stop sign or red light.
     
    #8 priustexasbob, Sep 9, 2010
  9. cproaudio

    cproaudio Speedlock Overrider

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    At warp stealth, does the HSI show that the engine is turning? red arrow from the engine? I remember seeing that the Prius was powered only by the battery at 65MPH, green arrow from the battery to the wheel and nothing else when I was driving on a slight downhill 30-35ft/mile descent.
     
    #9 cproaudio, Sep 10, 2010
  10. ken1784

    ken1784 SuperMID designer

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    I believe you mean the Energy Monitor screen.
    The red arrow means the engine is supplying energy.
    It is not a engine spinning status monitor.
    The Prius Plug-in does not spin the engine below approx 65 mph, but the normal hybrid Prius does spin the engine above 46 mph

    Ken@Japan
     
    #10 ken1784, Sep 10, 2010
  11. Tideland Prius

    Tideland Prius Moderator of the North
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    pakitt, at those speeds, I'd just cruise =). At speeds btwn 80-100km/h, I try to get into SHM (which is the happy mode you speak of where the engine drives the wheel directly). Above 100km/h, I would use cruise or try SHM.. if it works at those speeds. Warp Stealth wouldn't be too bad since you're not using too much power to maintain those speeds.
     
    #11 Tideland Prius, Sep 12, 2010
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