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Hills and mpg

Discussion in 'Gen 2 Prius Fuel Economy' started by gazz, Apr 26, 2007.

  1. gazz

    gazz Member

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    I live in the UK and travel 16 miles each way through country roads with little traffic, this is great for using all the driving techniques I have been reading about. I have been putting them into action and getting about 63 UK mpg which is great. The problem I have is that I know the car struggles on the hills, I have a scan gauge2 and am keeping the rpm to 2200 max. Has anybody got any thought on sacrificing a bit of gliding approaching the hill and taking a faster run at it. I have had a go at this and the mpg stays higher for much longer going up the hill.

    I know I can test this over a few tanks but was wondering if anybody had done any research on this subject.

    Thanks
     
    #1 gazz, Apr 26, 2007
  2. efusco

    efusco Moderator Emeritus
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    Absolutely a good technique I use on some hills.
    But it varies. If I can pull up the hill while maintaining an rpm within that rpm sweet spot of 1700-2300rpm without loss of significant speed I won't do a 'run up'.

    But if it's a longer and/or steeper incline then I'll begin a modest acceleration toward the hill using the 'sweet spot' rpm range so that by the time I reach the top I haven't dropped below whatever minimum speed while still holding rpm in the sweet spot.

    I have one and only one hill on my regular commute...on the way home...where I just can't quite do this. The approach to the hill is a sharp "S" curve bridge then the hill climbs quite steeply or a 1/2km or so. I usually have to get the rpm up to ~3000 to keep any speed at all by the time I crest it.
     
    #2 efusco, Apr 26, 2007
  3. gazz

    gazz Member

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    I have one and only one hill on my regular commute...on the way home...where I just can't quite do this. The approach to the hill is a sharp "S" curve bridge then the hill climbs quite steeply or a 1/2km or so. I usually have to get the rpm up to ~3000 to keep any speed at all by the time I crest it.
    [/quote]

    Would it not be better to hit the hill at a hight speed rather than go to 3000rpm?

    Also is there a minumus rpm to use does the sweet spot have minimum?
     
    #3 gazz, Apr 26, 2007
  4. JimboK

    JimboK One owner, low mileage

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    No research, just personal experience. I do much the same on certain hills: sacrifice some glide time to maintain or gain momentum for the next uphill, with the same goal as you of keeping RPM within its higher efficiency range. It sometimes creeps higher than 2200, in part because I can't safely or legally gain enough speed before beginning the climb. Much of it depends on traffic. I try to maintain a safe speed, and one not likely to incite road rage, at all times -- going uphill or not. On an isolated road with no traffic, I don't mind slowing down to below 20 MPH or so if I know there's a downhill on the other side. Unfortunately, traffic doesn't usually allow that on my typical routes.
     
    #4 JimboK, Apr 26, 2007
  5. efusco

    efusco Moderator Emeritus
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    <div class='quotetop'>QUOTE(gazz @ Apr 26 2007, 07:39 AM) [snapback]430389[/snapback]</div>
    Yes it would, theoretically, but my point is that the S-curve prevents me from increasing my approach speed significantly. I can pull the hill without exceeding 2300 rpm, but my speed drops to the mid-20s on 45mph speed limit road....at the crest of the hill the speed limit changes to 35mph though, so I don't mind dropping to around 30 and then accelerating up to 35 once I crest b/c then I can glide the next 1/2 mile to the next stop sign.
     
    #5 efusco, Apr 26, 2007
  6. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Hi folks,

    One thing, whether the target is 2,200 +/-200 rpm or 2,300 +/-100 or not to exceed 2,400, doesn't really matter as long as the goal is to keep the ICE rpm no greater than 2,400 and below:

    [​IMG]


    Excursion above 2,400 are not that bad until about 3,100-3,200 rpm, when we see a significant MPG impact. The ICE specific fuel efficiency noticeably goes down and the transaxle will mostly be in "normal" versus energy recirculate mode. Consider 2,400-3,100 to be an intermediate zone, OK for short durations but try to avoid sustained intervals in this range. Anything above 3,100-3,200 gets energy intense and should be avoided, traffic permitting.

    For those who don't have a tachometer or instrumentation, when we speak of a target rpm, it is a goal, not a hard limit. With practice, we can come close but don't think of it as 'dialed in' and some value we just 'go to.' There is 'slop' in the system, a range of rpms around that goal.

    In my own driving, I find MG2 torque to be especially helpful but this is pretty much limited to Graham scanners. I use it to keep in the 'energy recirculate' mode, which also keeps the ICE rpm pretty where I want it. For me, MG2 torque isn't quite as flighty as ICE rpm.

    Bob Wilson
     
    #6 bwilson4web, Apr 26, 2007
  7. alexstarfire

    alexstarfire New Member

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    It would seem to me, from the chart, that to get the best mileage that you wouldn't want to be in the 1700-2100 range as the throt%_recy is basically level in there. It seems you should want to keep the RPMs in the 1500-1700 range or the 2100-2350 range. You'd be in the sweet spot RPM wise and get the most energy back.

    Maybe I'm just too newb and am reading the chart incorrectly though. I don't exactly know what it means, but I think I get the general idea.
     
    #7 alexstarfire, Apr 26, 2007
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