Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55MPH)?

Discussion in 'Gen 2 Prius Fuel Economy' started by 2009Prius, Jun 17, 2010.

  1. FirstFlight

    FirstFlight Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    I don't have a scan gauge but it would seem like injector timing (fuel consumption) is the most relevant factor to fuel economy. Isn't it possible to figure out what the most efficient duty cycle is and just just that when climbing a hill? Just a thought....

    Anyhow, I've been thinking about getting a scan gauge but don't really want to spend the money. If I installed a tachometer, is it really useful for fuel economy or not worth the hassle of installing it.

    I want to install a mod that will tell me:

    1. If fuel is being squirted into the engine

    2. If the engine is spinning

    For number one, I was just thinking of running some wires to the coil of the fuel pump relay and putting an LED where I can see it. As for number two, the only thing I can think of is a tachometer. Any other ideas?

    Oh, sorry for hijacking the thread.....
     
  2. JimboK

    JimboK One owner, low mileage

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Are you channeling Hobbit? ;)

    See these papers where he describes both hacks:

    http://www.techno-fandom.org/~hobbit/cars/squirt/
    http://techno-fandom.org/~hobbit/cars/tachack/
     
  3. FirstFlight

    FirstFlight Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Awesome! Just what I was looking for, thanks!

    As a side note (I haven't read the hacks yet), I'd rather not use a tachometer. I'd just want to know the engine is spinning whether or not fuel is being used.

    So I'd need two LED's. One for consumption of fuel, the other to tell me the engine is spinning. I think I can make both of these work for me.
     
  4. uart

    uart Senior Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    That's why we're lucky in countries that use the L/100km units (Canada Australia and most of Europe). Because this gives fuel consumption resolution right down to 0.1L per 100km (equiv to 2352 MPG :eek:) you can always tell if there's any fuel injection going on. :D

    As for "2" just look at the speed. If it's more than 66 km/h (41 MPH) then the engine is spinning.
     
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  5. FirstFlight

    FirstFlight Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    And what if I'm below 41 MPH?
     
  6. uart

    uart Senior Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Well that's were the L/100km display comes in. If it reads anything above zero then it's injecting fuel and therefore the engine is spinning.

    With the MPG display unfortunately it will often max out at 100 even if there is a small amount of fuel being injected so you can't tell.

    As I said above the 0.1 L/100km resolution is equivalent to about 2352 MPG. :eek:
     
  7. FirstFlight

    FirstFlight Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Right. That's why I want to add a tach or LED.

    This one fits but it's kind of expensive.....

    http://cgi.ebay.com/ebaymotors/52mm...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories
     
  8. FirstFlight

    FirstFlight Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Now that I think about it, since the IGF wire is a 5 volt output (someone correct me if I'm wrong), I could just use a Microchip PIC to measure the pulse and output to an LCD screen. this would give me an accurate digital readout and a solution that's cheap. I'm gonna try it to see if it works.
     
  9. ystasino

    ystasino Active Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Just wanted to add that I have abandoned the sole use of the 15 kW metric for acceleration as I found it too aggressive. My SG II now shows iMPG (I don't want to have to look at the MFD, it is too distracting to look as often as I do) fWT, inj and SOC.

    Further, I wanted to note one good bug in SG II, that is the observation that iMPG with the engine spining defaults to a value of 9999. However, when the engine stops spinning below 41 MPH the iMPG value drops to approximately 4000<iMPG<1400 at 41 MPH or less. So no need for RPM! An additional advantage of reading the SG II iMPG value is allows me to simply check myself when going faster than my MFD tank average.

    Only have about 45 miles in the new tank so nothing to report yet.
     
  10. mikewithaprius

    mikewithaprius New Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    ystasino, very curious how your next couple tanks go, or at least highway trips. Let us know here?

    On a directly related topic, I met up with Hobbit the other day. Very cool guy! It was a huge help to me to understand (a little better, anyway) his highway style. Maybe it'll be of some help.

    Mike with a Prius: Prius-ing with Hobbit
     
  11. FirstFlight

    FirstFlight Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    So is it safe to assume that the goal is to keep it at 15kW? Nice write up by the way.
     
  12. mikewithaprius

    mikewithaprius New Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Yeah, basically, with the occasional slight deviations to 17-18 when necessary and the rare 20-25 kW for getting on the highway. Of course, my results weren't spectacular, but guessing from the results midway (mpg heading north) I have a feeling it was the terrain (mpg headed south after hills and accelerations to merge). I'd be very interested in others trying it and seeing how they do, since I don't have much chance to experiment - very little regular highway driving in my commute.

    It's taken me quite awhile to wrap my head around the concept of specific fuel consumption, but now, even though the lightbulb's only halfway on in my head, Hobbit's logic seems dead on. Least amount of gas for the most amount of power. Difficult to argue with that!
     
  13. FirstFlight

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    I'd be more than happy to try this for you. I got my Prius on 3/3 and I put over 3000 miles on it already. I just need to get a Scangauge and when I do, I'll let you know what I find.

    On a similar note, since I don't have a Scangauge, I tried keeping my MPG at 75% of my MPH when driving on the highway. I'm happy to report that over 120 miles (two 60 mile segments), my MPG is 62.3. My previous best over that mileage was around 55 MPG. So, it's working for me. My problem is that I live in a really hilly area but being able to squeeze out another 7.3 MPG was pretty impressive.

    And that's with the temps around 45 and 36 degrees respectively.
     
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  14. ystasino

    ystasino Active Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Thanks for the write-up, I enjoyed reading it. Other than a trip to Philly for which I had just refilled, one thing I have not invested in so far is to exclusively measure highway mpg. And with the weather in the 40s and 50s this makes a lot of difference.

    It's interesting that Hobbit is using the 15 kW spot, which as mentioned earlier in the thread is something I recently abandoned because I found it to be too aggressive.

    In terms of highway-only efficiency, I am now testing the SG II combination of mpg/inj rather than rpm/kW. My current approach is a hybrid of SHM and Hobbit's Super Speed Mode (HSSM) in that I will let the car roll to even 73 mph just before I enter a long uphill, which I will engage at 6.1 ms inj timing to come out of the uphill at 55 mph. If 6.1 ms isn't enough I will aim for the lowest possible inj timing that will take me to the top at 55 mph.

    Obviously HSSM has to do with maintaining momentum even at the cost of high RPM, which is the direct opposite of SHM. What my very preliminary understanding suggests is that in the reality of limited distance trips there are traffic and terrain circumstances in which the cost of maintaining momentum will be too high. Which is why I'm trying to customize the approaches for the specific terrain. I expect this experiment to last throughout the summer.

    My current tank has about 200 miles (55.6 mpg) that include about 4 or 5 20-minute city drives with cold engine, 10x8-mile one way trips to swimming pool (on highway, but in the beltway, avg speed of about 45-50 mph) 1x35 mile one way trip (avg speed 55-60 mph) and 2x35-mile trips to DC and back. Now all these trips vary: for example, the in-DC driving is great for a prius because of the low incline downhill roll in S4 while the cold-engine in city trips kill my mileage.
     
  15. ystasino

    ystasino Active Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    So I refilled at 435 miles, just reduced to two full pips, and at 57.0 mpg partly owing to the increase of temperatures helping significantly with gliding in the city. What I'm seeing is solidifying my belief that HSSM (Hobbit's Super Speed Mode) works when accelerating to 68 or even 70 MPH at 5.8-6.3 inj timings. However, when gliding things get complicated: What the declared floor speed might be will vary depending on two conditions, traffic and terrain.

    Let's assume a flat straight in which we are not limited by traffic. The most important consideration involves the speed we need to enter our next segment. If our next segment is downhill, then we can glide to low-ish speeds and expect to pick up momentum from the battery and against the air resistance. If our next segment is uphill we need to calculate how much momentum we need to go into the uphill with.

    The real question, and where I suspect I might have a different experience from Hobbit, is what to do if our next segment is severely uphill where his calculated 15 kW are simply not enough to maintain momentum. In his write-up he proposes to even go as far as 2800-3000 RPM to maintain momentum if needed. My preliminary experience varies and suggests to sustain 15 kW or the lowest possible power demand from the ICE to maintain decent momentum.

    In the above scenario, Hobbit's method will have you be atop the hill at 66 MPH with significant consumption of fuel, while my approach will have you at 50 MPH, but having consumed less fuel. Hobbit's approach will have you glide whenever the compensatory downhill (that will necessarily follow the wasteful uphill) comes, my suggestion will have you accelerate through that downhill at an energy efficient way until you reach 68 MPH or so where you can start gliding.

    I suppose the optimal approach might vary depending on when the compensatory downhill comes, if it comes long after the uphill then Hobbit's approach will get you were you want to go faster.

    The only way we can really ever test this is to have two Prii try these two uphill climbing techniques. Driver A would try technique 1 and 2 and Prius B would try technique 1 and 2 as well. Both Drivers should be at one Prius at a time. Should be able to come to a conclusion about this that way...
     
  16. mikewithaprius

    mikewithaprius New Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    It's still a very rare day to use this, though. It seems like more of a footnote to me. Even with quite steep bridges and hills around here, 2400 RPM is the absolute max I hit only on rare occasions. Hobbit was quite focused on staying under 2000 RPM most of the time, so it seems like that's more of the general operation RPM ceiling with his model.

    For your proposition, I'd like to test it for my commutes, but in this area it might too congested to safely try a large acceleration to the base of a hill and then slow considerably by the top.

    I agree that a mix should be necessary. There's this brilliant little segment of 50 mph driving I do of about 2 miles. There are these little humps in the road, but basically I can use tons of warp stealth, and keep 50 mph by jumping into a very light acceleration for a couple seconds only. I see no practical benefit to making these short burns at the 15 kW range, since I don't need that speed, and I would hold them for the same amount of time anyhow, so I use SHM, and can easily get over 100 mpg on those two miles (of course, the two miles prior - ohh, the uphills!).

    I'm not getting why you need two Prii but just one driving at a time. To make sure it works across multiple machines? I've been considering a DC trip at the end of the summer, I'll let you know if that's the case and we'll find some empty road at 4am :D
     
  17. ystasino

    ystasino Active Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    I'll be interested in your findings, but just wanted to clarify that I am only talking about conditions where 65 MPH is the posted speed limit, not smaller suburban roads.

    One thing you might also want to try is to have SG show you both inj and kW. I'm finding that 15 kW usually corresponds to about 6.4 ms at these speeds and that ideally I accelerate at 12 kW (~6.1 ms).

    As far as my tanks go, I think that at 57 mpg with temps in the 40s and I95 traffic I'm hitting the ceiling of efficiency. Obviously this should increase with the increasing temps. As far as "highway-only" consumption measurements I might do them, but do not think they are accurate, because the *real* 65 MPH-only/low traffic conditions are very short making consumption measurements unreliable especially given the Prius's inability to provide measurements of absolute gasoline consumption, due to the bladder.

    So if I get 57 mpg/tank in the winter and 61 mpg/tank in the summer that keeps me happy.

    The reason I was suggesting two drivers/car/route/method was so that both proponents of method A and method B get a better understanding of what they other is doing, reading it on a forum is slightly different.

    Again thanks to Hobbit for his highway efficiency article showing that the Prius is a highly efficient car in normal highway, as opposed to SHM, speeds.
     
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  18. plastermaster

    plastermaster Junior Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Hello everyone! This is my first post on this forum which I just found the other day in my research for new tires. It is wonderful to find others with OCHD :) (obsessive compulsive hybrid disorder). I am enjoying this thread on driving technique. Question though, can someone tell me what "super highway mode" is? is this something that is a feature on some Priuses (not my 2007) or is it a mode of driving like pulse or glide?

    BTW I liked the paragraph about cruise control on the sweet spot article. It reminded me a bit about a post extolling the virtues of all SUVs having mandatory standard transmissions. Sort of a way to "earn the right" to impose them upon our shared highways and parking lots, and to discern between those who REALLY value their (assumed) safety advantages and those who merely site safety as an excuse. It was in humor of course.
     
  19. donee

    donee New Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Hi Plastermaster,,

    I had typed out a multi paragraph explaination of SHM. But PC decided to boot my login, and it was lost...Maybe somebody else will explain it to you...Otherwise, just search SHM on Cleanmpg.com .....
     
  20. magic-man

    magic-man New Member

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    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Tried this out on the way to work today. Definately gave better MPG! Made some mods to my normal routine:
    NOW:
    I now only use Cruise Control on long flat cruises AND in the 'double fine' zones (just in case).
    I use a +2 -3 strategy for speed control... My Speedo says 67 when I am going 65, so I allow the speedo to get to 69 downhill and 64 uphill, 67 on flats.
    Don't have a tach, but use the listen method... If I hear the engine roaring, it is over 2000 rpm... Basically, I am maintaining the lowest RPM possible while climbing the hills with the -3 range.

    Made a +3 MPG difference on the 45 mile drive to work!

    If you are using a gentle pedal in the city to see how far U can go with EV, then you already know the gentle pedal adjustments needed for p&G at 65 MPH.
     
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