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. 2009Prius

    2009Prius A Wimpy DIYer

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    Just got pointed to this recent writing by hobbit:
    Sweet spot refinement
    from another thread:
    Well, one has to be curious when you say you get better fuel economy at 66 ~ 68 MPH than 50 ~ 55 MPH! :)
    So if I understand correctly, you found that pulse and glide at higher speeds (66 ~ 68 MPH) is more efficient than super highway mode at lower speeds (50 ~ 55 MPH), right?
    Was 66 ~ 68 MPH the peak speed or the average speed? If peak then what was the average speed which you got 70 MPG at?
    Thanks very much!
     
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  2. 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 2009Prius,

    Going to be pretty tuff to beat 75 mpg (SMH at 50 mph on a warm day).
     
  3. bisco

    bisco cookie crumbler

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

    that was a very enlightening article, thank you H! the 20% i understood makes sense and yes it is counterintuitive. i will begin practicing tomorrow. i have also had some success accellerating smartly from a stop to 30-40 mph depending on limit. it is surprising to see avg mpg climbing slightly as i get better at it. i do think a tach or scangauge would make it easier.:)
     
  4. andyprius

    andyprius Senior Member

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

    I also Thank Hobbit for his mind boggeling post. I did try it today on I 50, which is a slow downhill grade to the Delta and the confluence of the American and Sacto River. I was probably a bit aggressive and took the car up to 70 and 75 once. This section is composed of mild ups and downs with the overall elevation decreasing to about sea level. The round trip was 24 miles to Mather exit, I got 52 mpg going and 49.9 returning. The return was of course uphill, again taking advantage of any rolling hills that occured. This was done warmed up, tanked up, with a 1 hour layover between going and returning. Since I have always been a 55mph guy I was amazed at the overall mpg. Of course keeping the car in stealth forever was the object, which when the Sun is on the MFD one cannot be totally sure. Mostly I use pedal feel anyway. The surprising thing was I discovered I could keep the car in stealth even longer when slowing for traffic or exiting. No more Cruise Control, I guess.
     
  5. 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

    First, this seems to be partly an apples-to-oranges comparison. Hobbit makes regular reference to warp stealth and at least modestly hilly terrain. SHM is best done on level terrain or nearly so where WS is useful only as a long slow (and efficient, I might add) deceleration technique.

    But .... SHM aims to keep the ICE near the low end of its RPM range and presumably well below 15 kW -- and is useful (if at all) at <55 MPH. Hobbit does seem to be suggesting that running at somewhat higher power and speed is more efficient. I'd like to hear from Hobbit to see how he might reconcile the theory and his experience with the results of the SHM practitioners.

    Meanwhile, my CAN-View shows ICE power in kW (something I've rarely used up until now), injector timing, and ignition timing (the holy grail of instrumentation for SHM folks). I don't think I can display them all simultaneously, but I might play with ICE power a bit and see what the correlation is between these and with ICE RPM.
     
  6. tesla440

    tesla440 Junior Member

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

    Not to through more into the mix, I guess I've seen what Hobbit is talling about. But not at the MPG as he is getting.

    By watching the MFD, I've been able to average 57.6MPG on a 300mile trip at speeds 66-68mph while taking advantage of hills & some drafting when possible. It does seem to have a sweet spot there, like at the 55-58mph that I've seen. I don't have a scangauge to tell you any more than what the MFD can show for instantanious mpg.
     
  7. SageBrush

    SageBrush Senior Member

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

    Sometimes something tells me the car is in its comfort zone. I'm not even sure why I know it. My brain says "high torque, low rpm," but what am I hearing or feeling ?

    Some may find "P&G" at highway speeds to mean something in trying to duplicate Hobbits results, but I think more along the lines of "high gear or fuel injection-off." I tend to think his stellar results occur because he has learned to jump into and out of high gear quickly, while most of us are suffering through inefficient slow transitions of the CVT. It is probably not coincidence that the practical advice to "let off the pedal a bit" to enter a low rpm-high-torque running state is the same thing we do to enter stealth mode.
     
  8. 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

    Any new data on this? Not necessarily about beating SHM, but about being a highly efficient way of driving.

    I've been getting around 54 MFD mpg on rather hilly highway interstates I83 and I95 around Baltimore and between Baltimore and DC. Something's telling me that 54 mpg with speeds varying between 50 and 62 MPH with temps and tires in the 40s isn't optimal.
     
  9. PriusSport

    PriusSport senior member

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

    I think there is something to this. I find my highway mileage improves going 70-75 mph instead of 55-60 and letting up on the gas a bit when there is a downslope.
    This gets more of the battery mode working, and maybe increases the kinetic energy through the wheels.
     
  10. 2009Prius

    2009Prius A Wimpy DIYer

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

    For this particular subject I haven't seen any new data, or any rigorously collected data ever, for that matter. One thing we are sure is that it is best to minimize the current going in and out of the HV battery, since the conversion loss is significant.
     
  11. 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

    This might be self-understood for many posters here, but the engine does not warm up as fast with hard acceleration and slow deceleration. While cold the engine will not spin empty at 960-992 RPM, but faster consuming gas and having an impact on mpg.

    So if anyone is trying any such method, be sure that your car's engine is warmed up, before you start with this.
     
  12. 2009Prius

    2009Prius A Wimpy DIYer

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

    The higher the RPM, the more the fuel burned, thus the faster the warm up. When the engine is cool I would pulse harder to accelerate the warm up. I also warm up by remaining at park during stage 1A.
     
  13. 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

    But if you're trying to accelerate hard and quick and then glide for long stretches the engine will not warm up as quickly as if you accelerated slowly at around 1600 RPM for longer periods of time.

    At least that was my experience yesterday during which my entire 9 mile route on the highway the engine never warmed up and it was spinning at ~1150 RPM when gliding, in contrast to every previous day I would accelerate slowly during the same route and reach the 960 RPM spinning condition halfway through the trip.
     
  14. 2009Prius

    2009Prius A Wimpy DIYer

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

    I see. Sounds like you need to block the grill.
     
  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 programmed the XGauge for measuring injection timing as suggested by hobbit here Sweet spot refinement

    The idea was to see whether P&G at higher speed was anywhere near as efficient as super highway mode. I drove the car 30 miles from and 30 miles back to Baltimore, at night so that there was not much traffic around. The ambient temperature was at ~36F, tire pressure at 44 psi on the stock integrities. There was no wind this evening. The FWT was between 184-188 F throughout these readings.

    As I understood it, in his article hobbit tries to combine three distinct tactics to improve highway efficiency. First, to accelerate hard at ~3000 RPM until just before the hump of the uphill, second, to maintain highway speeds at injection timing from 5.8 to 6.3 ms (~15kW) and third to glide at 960 RPM when going downhill.

    During my experience this evening, it was impossible to corroborate the first and third assumptions. I believe that has to do with how steep the terrain is from Baltimore City to 30 miles northwards. Simply put 3000 rpm killed my mpg so much that it was impossible to recover gliding downhill. Further, the downhill glide reduced speed to 53 mph making it impossible to regain momentum in an energy efficient way.

    On my way back from the first 30 miles from Baltimore, I decided to scrap the hard pulse and soft glide ideas. In any case the more interesting parameter to watch was the inj timings and particularly their relationship with RPM and gallons per hour. Ignoring the 3000 rpm acceleration idea on my way back and without any gliding the maintenance of these injection timings at highway speeds resulted in more than 55 mpg, a full 3 mpg higher than with the hard pulse and soft glide. As these timings were held constant between 5.8 and 6.3 ms, the car speed somewhat followed the terrain and the RPM did not generally exceed ~1630. This seems somewhat more efficient and precise than simply monitoring RPM, but I will definitely need to repeat this driving towards Philly and DC. It is also consistent with the rough guide of keeping the RPM between 1400 and 1600 at highway speeds. Whenever hard acceleration was needed I would use as much gas so as to slowly lose speed and not trying to overpower the terrain at 3000 rpm.

    So for hilly terrain and highway speeds the key is to expect how much gas you need before heading uphill and to adjust the uphill entry speed and entry RPM accordingly from the previous segment (flat or down hill) so as to not crawl to the top, but also without trying to overpower the terrain.

    All suggestions and ideas are welcome.

    Just to add that it is unsafe to drive between 50-55 MPH at the heavily congested I-95 during normal hours, so I am searching for the best way to drive without killing traffic or mileage.
     
  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

    ystasino (and others),

    I also had a very hard time achieving good results on the highway trying this technique with higher speeds, consistently getting down in the lower 50s.

    Terrain really has tons to do with it, since any hills seem to erase what downhill/flat gains you have, like ystasino said.

    I was able to, though, on a road between about 43 and 50 mph, get similar results using the techniques Hobbit described, so I thought I'd summarize them here.

    Of course, this isn't highway driving, but still faster than pulse and glide - but that was the interesting part. I got better mileage driving between those speeds than P&G on the same stretch. I think part of the reason is that I did this in cold weather, and in cold weather after long glides, the ICE is going to be quite cooled off and not running optimally, so my pulses probably had lower mpg by a good deal compared to warm weather.

    There were slight ups and downs but largely flat terrain. I was able to stay in SHM most of the time, and then tried to use warp stealth as much as possible, even if only for a few seconds, but often as long as I could stand. When I felt I was getting toward the the lower edge of my speed range, I'd flip into SHM and then gradually accelerate back up out of SHM. I tried to keep the "bursts" to a minimum, since I had experienced that mpg-reducing problem on the highway. I figure even if I am pulsing at 40 mpg, and can then warp stealth for half the distance of that pulse, that's 60 mpg. At higher speeds you can usually slowly gain speed at, say, 40-50 mpg easily, so combining, for example, .4 miles of 50 mpg with .2 miles of warp stealth is 75 mpg. Results were over the first half of the trip (so 10 miles for the half) it was in the low 60 mpgs. Keep in mind this was after your typical warmup phase, in the city before getting on the highway, so the average for the faster-than-P&G section was easily up in the 70s, with some five-minute bars looking like P&G way up near 90-100 mpg.

    tldr: 1. Warp stealth as much as possible, even if a couple seconds. 2. Gradual acceleration with relatively high instant mpg instead of bursts. 3. SHM as much as possible in all other cases.

    It was a pleasant surprise since I was forced into this experiment by lots of traffic, and had to keep up with the flow. Good to see you can drive completely with everyone else at somewhat faster speeds and still get this.
     
  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

    The short story/numbers:

    - Daytime 95 miles @ 55 F to Philly => 60.9 MFD *highway* MPG/61.8 MFD total MPG
    - Nighttime 95 miles @ 43 F back => 54.2 MFD *highway* MPG/ 55.8 MFD total MPG
    Combined MFD mpg 58.8*
    Driving time 110 minutes/leg , which is about 10 minutes slower and 10 mpg lower than driving at ~74 mph.
    -44 psi
    -Breeze
    -Religiously between 5.8 and 6.3 ms injection timings when possible.
    -Gliding as much as possible when going downhill
    -Not surpassing 2400 RPM (between 6.7 and 7.3 ms) when going uphill
    -Floor speed 57, average highway speed ~62-63 mph, operating at 66-68 mph frequently
    - Driving alone with a full bladder (~9 US gallons, I think)

    * The discrepancy in the MPG between the two legs of the trip have to do with: a) daytime driving allowing for more precise evaluation of uphills and downhills, b) different ambient temperatures and possibly c) terrain, which may involve different uphill and downhill inclines on the two legs of the trip.

    I think that driving up to 3000 RPM is the only idea I would ask hobbit to reconsider, otherwise this trip supports his finding of the 66-68 mph range as an efficient way of driving on the highway. MD highways have a lot of hills, and I expect that hobbit's observations would lead to better mpg than what I got on a flatter terrain.

    I will update if and when I get better figures :)
     
  18. 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

    I'm in the midst of a significant career change (retiring from one job, preparing for school for another, and an out-of-town part time job in the meantime), which will see significantly greater highway travel. I'll have to revisit the plethora of highway driving indicators I have in CAN-View to see what I can add to this discussion.

    You're pretty close with 2 and 3. Hobbit is not recommending using 3000 as a routine uphill target, but instead only as necessary to maintain a safe speed on an uphill:
    When using RPM as an indicator, he reports that "the 15 kilowatt region nominally occurs around 1900 - 2100 RPM," and suggests, for those with a tach, using 2000 as a "basic target" unless the incline absolutely requires more to remain safe, legal, and courteous.

    So your experience doesn't contradict Hobbit's; it validates it.

    It's tough in your conditions, no question. I agree that that's probably too low for safe driving on I-95. I generally hold it to at least 60, though that's dynamic and dependent on traffic at any given point; I keep a close eye on my mirrors. When I make the occasional drive to Maryland, I generally resign myself to 60 MPG at best in warm weather.

    And possibly d) the breeze. It's remarkable how much impact even a small breeze can make on fuel economy. A 5 MPH wind can add or subtract up to 8% depending on its direction relative to yours.
     
  19. telmo744

    telmo744 HSD fanatic

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

    Past week I have tried a similar driving technique with my 3Gen 17".
    On highway did not went so well as I expected. On a 200mile trip with 70MPH "target" gave me 47MPG, which is about the same as a cruise control trip.
    IMPOV, I think the part throttle operation in the 3Gen is very satisfying, beating "warp stealth glide". Obviously lower speed P&G still remains the only way to good hypermile.
     
  20. 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

     
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