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. sorka

    sorka Active Member

    Joined:
    May 9, 2008
    858
    102
    0
    Vehicle:
    2009 Prius
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    I've been working on this for the last week but am not having much luck. I'm able to monitor my RPMs. However, at freeway speeds, it takes like 25 seconds to get from 63 to 68 MPH at 2K RPMs. When I go into glide (no arrows in or out of the battery), the speed drops from 68 to 63 in about 5 seconds, so I spend most of the time lightly accelerating at 2K RPMs. My fuel economy plummitted while driving like this.

    What am I doing wrong?
     
  2. ystasino

    ystasino Active Member

    Joined:
    Apr 17, 2007
    791
    47
    0
    Location:
    Tucson, Arizona
    Vehicle:
    2007 Prius
    Model:
    Two
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    First of all, we don't know how long your sample route is, what temperatures we're talking about etc.

    Second, you do not need to worry for the "no arrows" condition after 41 MPH, it won't save you anything. Use the "yellow arrows" condition, that's what we term gliding above 41 MPH (i.e. with the engine spinning at ~960 RPM). The electric energy from the converter will be able yo glide your car for more than 5 seconds.

    Third, RPM is not a very good way of measuring efficiency. There is plenty of debate at what is the best metric, but we all agree that RPM isn't that one. Those trying slower speeds of super-highway mode use the scangauge IGN number 14. Hobbit whose articles are often cited in this thread uses the xGauge (custom programmed scangauge command) kW number 15. Other's use the xGauge inj number 6.1.

    Fourth, there are two components to this technique, knowing when to accelerate and when to glide. Accelerating efficiently is very important and as stated in teh above paragraph a source of contention. All these metrics will give you good numbers I'm not sure which one will give you the best. There will be uphills where IGN 14 is way too weak, inj 6.1 is just right and kW 15 is too much. Generally IGN 14 is recommended at flat terrains and speeds up to 50 MPH, after that the NHW20 simply doesn't have the power to beat air resistance at that engine speed.

    Knowing when to glide (yellow arrow condition above 41 MPH) is a matter of experience with the terrain and recognition of the downhill's steepness and length. Gliding when there is no slope will just result in you losing your momentum for very little gain.

    Fifth, this will all make sense when you buy a SG, and program these xgauges in. It really is simple, but it also requires you reading this subforum extensively. Let us know how you are doing.

    Before SG I had ~ 48 mpg in the winter
    After SG I had ~54 mpg in the winter
    After SG with xgauges programmed I had 57 mpg in the winter
    After SG with xgauges, higher temps and refinement I am at 62.4 mpg in my current tank though I'm going more slowly than I ideally want.
     
  3. mikewithaprius

    mikewithaprius New Member

    Joined:
    Jan 5, 2011
    656
    103
    6
    Location:
    Rhode Island
    Vehicle:
    2007 Prius
    Model:
    N/A
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    sorka, this is a bit different than standard pulse and glide in regards to duration of burns. You will be accelerating a lot more than you think is possible to get better mileage. Unlike P&G where you try to avoid the engine at all costs, it's OK for a "pulse" to last even a couple minutes in this sort of highway driving. I was very surprised how much Hobbit used the engine, and how long and hard the pulses seemed. It will all be offset by warp stealth use.

    Secondly, you want yellow arrows showing in the "glide", so it will be warp stealth. Only use it in situations when you won't slow down quickly, i.e. downhill, or to control speed on flat surfaces. It definitely won't work uphill.

    Thirdly, it sounds like you have Scangauge, so program in kW and shoot for 15-17. Ignore RPMs for now. Alternatively, and much easier, just do instant mpg at 75% of current mph while up at speed. It's a surprisingly accurate way to get the sweet spot without much Scangauge tinkering.

    Hope that helps.
     
  4. ystasino

    ystasino Active Member

    Joined:
    Apr 17, 2007
    791
    47
    0
    Location:
    Tucson, Arizona
    Vehicle:
    2007 Prius
    Model:
    Two
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    So my last tank was 62.7 MFD mpg for 535 miles. That was aided by two great trips to the DC area with many many miles of gliding, but also included a city trip in the cold rain which required a lot of defogging and dropped my mpg from 62.9 @200 miles to 59.3 mpg.

    I have now resorted to using the following scangauge parameters on the highway: iMPG, IGN, kW and inj. The reason it's important to monitor all four is two-fold, that I seek to realize which one or which combination is the best, and that I compensate for the poor refresh rate of SGII.

    I have attempted to "pulse at 18 IGN", "hold at 14 IGN" and glide at 5 IGN. Horrid SGII refresh rate aside I find these measurements as good overall indicators of efficiency on a flat terrain. For hilly surfaces they are rather coarse and the SG refresh rate is absolutely aweful for any real correlation of efficiency and IGN rating: by the time you're halfway uphill and know that you are pulsing with 16-17 kW, the IGN gauge still shows 15! Or when you are gently pulsing with 13 kW IGN might show 19! It's just woeful for hilly terrains

    So having glanced at the kW output while also observing IGNs they are a more refined, but perhaps harder to follow, way of tracking efficiency. On a flat terrain it's fairly straight forward to conclude that ~10 kW correspond to 14 IGN and at 60 MPH give an iMPG of about 1.5x the MPH. On a flat terrain ~15 kW correspond to about 18 IGN.

    Now when we go uphill speed and efficiency are dictated by the terrain. In these situations I use kW and inj timings without being shy of hitting 18 kW/19IGN/6.8 ms inj.

    So what's the conclusion? The only conclusion I have reached so far is that all three measures that hypermilers use seem to be working, but none of them alone can get me the most efficient mileage.

    IGN may be the most useful metric on a flat terrain, because the SG refresh rate is irrelevant and IGN provides a single and simple indicator to use. kW output/inj ms may be more accurate, but require more attention to optimize for a particular terrain. I see myself using all 3 for the foreseeable future and wish I could also have two more indicators to monitor SOC and fWT. After using all these parameters, I find the use of RPM as mostly meaningless.

    Any comments and suggestions are appreciated.
     
  5. mikewithaprius

    mikewithaprius New Member

    Joined:
    Jan 5, 2011
    656
    103
    6
    Location:
    Rhode Island
    Vehicle:
    2007 Prius
    Model:
    N/A
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Thanks, this is great - could you remind us, what is your percentage of highway driving on this tank? Maybe better phrased, how much is over 42 mph?
     
  6. ystasino

    ystasino Active Member

    Joined:
    Apr 17, 2007
    791
    47
    0
    Location:
    Tucson, Arizona
    Vehicle:
    2007 Prius
    Model:
    Two
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Hmm, this is hard to estimate, but obviously very relevant. here are my estimates:

    Last refueled on 04/07, or 18 days ago.

    Speeds 42-54: 265 miles. These segments yielded about 61 mpg
    Speeds 55-65: 170 miles. These segments yielded about 60 mpg
    Speeds < 41: 110 miles. These segments yielded about 65 mpg. This last segment is the average of different short trips inside the city or long glides in S4.

    The tank I refueled this morning is probably my last one with such numbers. My almost daily 8-mile short highway trip to the pool will end on Labor day after which at least 200 of the above miles (42-54) will not be logged for the entire summer.
     
  7. mikewithaprius

    mikewithaprius New Member

    Joined:
    Jan 5, 2011
    656
    103
    6
    Location:
    Rhode Island
    Vehicle:
    2007 Prius
    Model:
    N/A
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    VERY cool, 80% of your driving over glide threshold and around 60 mpg MFD is awesome! More confirmation of the viability of the technique. Use of IGN is good info, too, since I know I haven't been big on pulsing at 15 kW during the many times when I don't need more speed (15 kW) but can't afford to lose any either (warp stealth). The middle ground of IGN 14 seems perfect, and is something I already do sort of naturally, like we talked about in that message.

    Keep doing what you're doing.
     
  8. ystasino

    ystasino Active Member

    Joined:
    Apr 17, 2007
    791
    47
    0
    Location:
    Tucson, Arizona
    Vehicle:
    2007 Prius
    Model:
    Two
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    I'm wondering if someone who knows a lot about the physics behind IGN, kW, inj at different speeds could come up with a single metric that would solve this in a device that would refresh faster.

    I wonder whether pEEF would be up to the challenge :D
     
    1 person likes this.
  9. mikewithaprius

    mikewithaprius New Member

    Joined:
    Jan 5, 2011
    656
    103
    6
    Location:
    Rhode Island
    Vehicle:
    2007 Prius
    Model:
    N/A
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    I'm insanely excited. After months of 60 mpg highway mileage eluding me, I got 62.5 mpg (calibrated Scangauge mpg, NOT overestimated MFD mpg) this morning over 50 miles. I could barely get better on the way home with pulsing and gliding with all the stoplights. Have so much to do today and am dying to write more about it, but it will come later.

    Very excited about the prospect of taking a road trip and not having to pulse and glide across the country :)
     
  10. mikewithaprius

    mikewithaprius New Member

    Joined:
    Jan 5, 2011
    656
    103
    6
    Location:
    Rhode Island
    Vehicle:
    2007 Prius
    Model:
    N/A
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    ystasino,

    On that first thing, my experience today was wonderful with IGN 14.

    Secondly, my problem on the highway, is exactly that - not pulsing at the opportune time. Since it seems to be a weakness of mine, it was great to see aiming for IGN 14 basically wipes that out of the equation.

    A basic summary of what I did today is this:

    -hold at IGN 14, more rarely 15 if needed. Don't slow dramatically, stay pretty much same speed
    -pulse at 15-18 kW if needed for short time
    -warp stealth sparingly, only when it wouldn't slow my momentum much, or at all, like on steep enough downhills

    Since I have the feel for 15-18 kW at this point, all I had to monitor was IGN. Even if it's a couple mpg below the maximum potential with other techniques, it was so easy and relaxing to do that this is my new default highway driving style.
     
  11. ystasino

    ystasino Active Member

    Joined:
    Apr 17, 2007
    791
    47
    0
    Location:
    Tucson, Arizona
    Vehicle:
    2007 Prius
    Model:
    Two
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    That's what I'm using too. Perfecting this requires knowledge of the terrain so that you go to 18 kW before a steep uphill and leave 18 kW just before reaching the top. Even more crucial is knowing when to WS or go to IGN 14/8.0 kW by judging the depth and steepness of the downhill. This becomes harder at night, however traffic is less of an issue then.

    I would suggest to not use IGN however, because it doesn't have decimals and because SG approximates it during pulses and glides. These approximations and the horrid refresh rate have me looking at both kW and inj.

    (Was at 63.7 mpg yesterday before I went out for a night in the town, now back to 62.9)

    EDIT: tried to accelerate hard (25-30 kW) on the way home in a very familiar 6-mile highway stretch today and while it wasn't a disaster, the results weren't as good as 15-18 kW acceleration. Maybe the relatively cool temps were a problem, but I doubt it.
     
  12. donee

    donee New Member

    Joined:
    Aug 15, 2005
    2,956
    193
    0
    Location:
    Chicagoland
    Vehicle:
    2010 Prius
    Model:
    III
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Hi Mike,

    SHM on level terrain is hard to beat, as you found out. I commonly did three 75 mpg plus bars during the summer on my highway half of my commute in my 2nd Gen Prius.
     
  13. ystasino

    ystasino Active Member

    Joined:
    Apr 17, 2007
    791
    47
    0
    Location:
    Tucson, Arizona
    Vehicle:
    2007 Prius
    Model:
    Two
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Thing is that SHM only works for those in flat terrains and IGN is not a refined enough parameter for those of us negotiating hills, it refers to a range of power output from the ICE that makes a significant difference in mpg.

    For the record my newest tank had 63.0 mpg at 516 miles in 10 days of driving. This was achieved as follows for the most recurrent and lengthy trip of my tank:

    Accelerate mildly at 12.0 kW
    Accelerate as close to 12.0 kW as possible depending on your terrain and desired speed without allowing the vehicle speed to drop below 45.
    Decelerate mildly at 8.0 kW
    WS at lengthy or steep downhills.
    Accelerate before the incline starts so that you don't need more than 18 kW to reach the top of the hill.
    Decelerate just before the hump of the hill.
     
  14. 2009Prius

    2009Prius A Wimpy DIYer

    Joined:
    Mar 25, 2009
    2,701
    476
    63
    Location:
    USA
    Vehicle:
    2009 Prius
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Great! What was the overall average speed of those trips? Thanks!
     
  15. ystasino

    ystasino Active Member

    Joined:
    Apr 17, 2007
    791
    47
    0
    Location:
    Tucson, Arizona
    Vehicle:
    2007 Prius
    Model:
    Two
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    I wish I knew, if I showed you my terrain which I am trying to export from the My Tracks android app you would see why it's harder than it looks.
     
  16. 2009Prius

    2009Prius A Wimpy DIYer

    Joined:
    Mar 25, 2009
    2,701
    476
    63
    Location:
    USA
    Vehicle:
    2009 Prius
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    An alternative would be just use one of ScanGauge's built in functions to read back the average speed for each trip, just a few button pushes. Yet another option is to manually calculate mileage divided by travel time. Both would include some stop time during the trip but if your trips are mainly highway then that shouldn't affect much. Without this data it would be difficult to compare the MPG numbers.

    Now I think of it if the app is any good it should give you the average speed at the end of trip also.
     
  17. ystasino

    ystasino Active Member

    Joined:
    Apr 17, 2007
    791
    47
    0
    Location:
    Tucson, Arizona
    Vehicle:
    2007 Prius
    Model:
    Two
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    I don't think that my average speed will tell you anything but here it is.

    http://priuschat.com/forums/gen-ii-...-help-fuel-economy-questions.html#post1324373

    Here's the data from a recent trip, make sure to click the link to give you an indication of the terrain levels. The axes are unfortunately in relative units.
     
  18. 2009Prius

    2009Prius A Wimpy DIYer

    Joined:
    Mar 25, 2009
    2,701
    476
    63
    Location:
    USA
    Vehicle:
    2009 Prius
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Thanks! I would say the data tell us a lot! Especially the average moving speed, but also the average speed and max speed. Elevation gain/loss will be averaged out over several trips assuming you are traveling around the same area. So is this a typical driving condition that you averaged 63 MPG over 10 days?
     
  19. ystasino

    ystasino Active Member

    Joined:
    Apr 17, 2007
    791
    47
    0
    Location:
    Tucson, Arizona
    Vehicle:
    2007 Prius
    Model:
    Two
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    The data doesn't show you anything about how steep my climbs are. Anyway here's a photo of the MyTracks app graph showing the trip to my destination, the return is backwards. For both legs I average 63 mpg, blue is speed, green is elevation.

    [​IMG]

    Total Distance: 12.29 km (7.6 mi)
    Total Time: 18:17
    Moving Time: 15:11
    Average Speed: 40.33 km/h (25.1 mi/h)
    Average Moving Speed: 48.52 km/h (30.1 mi/h)
    Max Speed: 88.34 km/h (54.9 mi/h)
    Min Elevation: 18 m (59 ft)
    Max Elevation: 82 m (268 ft)
    Elevation Gain: 82 m (269 ft)
    Max Grade: 4 %
    Min Grade: -5 %
    Recorded: Tue May 10 19:28:02 EDT 2011
     
    1 person likes this.
  20. 2009Prius

    2009Prius A Wimpy DIYer

    Joined:
    Mar 25, 2009
    2,701
    476
    63
    Location:
    USA
    Vehicle:
    2009 Prius
    Re: Pulse and glide at higher speeds (66 ~ 68MPH) beats super highway mode at lower speeds (50 ~ 55M

    Thanks again! Sorry if I missed it earlier. What's your tire pressure?
     
Loading...