Want to know more about Driving with Load (DWL)?

Discussion in 'Fuel Economy' started by desdemona, Aug 7, 2007.

  1. desdemona

    desdemona Well-Known Member

    Hi,

    We have lots of hills-- and a lot of times there isn't all that much traffic. This concept makes a lot of sense here. I want to learn more about doing this. I know the basic concept, I think. You keep a steady acceleration and don't accelerate up the hill (unless necessary I guess) and basically you could NICE-on coast if you wanted down (if the hill goes down enough).

    Any thing else for a newbie hypermiler.


    --des
     
  2. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

    Yes, don't think of it as a steady acceleration up the hill. Think of it instead as trying to keep the engine using the same amount of gas on the way up and letting gravity assist you on the way down so you use less gas. The best approximation to get you going is it keep a steady pressure on the gas pedal. Sort of like the poor man's cruise control in the old VW Bus where you would wedge a pine board against the pedal to maintain speed. All that really did was maintain a pedal position. The result? You would go slower up a hill and faster down the other side.

    Try that as a start. If there really isn't anyone around, the most efficient way to crest a hill is with just barely enough momentum to get you over it. If the car can FAS this is ideal. If not, just let it get down to the speed that is still more efficient than idle consumption and coast over in neutral (if possible).

    I generally will ease off the pedal a bit with moderate hills so I use less gas going up, then coast as much as possible on the other side. Sometimes that means I have to give it a quick acceleration at the top and then coast as far as I can down. Approaching a hill you want to accelerate on the flatter land as then you aren't spending even more gas fighting gravity on your way up the hill.
     
  3. hobbit

    hobbit He who posts articles

    Sometimes pushing just a little harder helps keep speed more
    even over hills, but I consider that there's probably a range
    that staying inside of will roughly equate to "pure" DWL and
    still return better MPG than blasting up hills. The Prius
    certainly exhibits such a range, up to maybe 2400 rpm and
    the Prius control strategy always keeps the engine in a high
    torque scenario so it's sort of automatically DWLing in high
    gear all the time anyways. I think it would help to clarify
    exactly what is meant by "with load" in the spirit of the
    original definition, since several discussions seem to
    advocate very *light* loads [low torque?] as part of this and
    yet we know that higher torque tends to keep an engine
    higher on the BSFC map. In other words, which is it??
    .
    _H*
     
  4. tbaleno

    tbaleno Well-Known Member

    That might have to do with the CVT and motor being able to compensate, but for a normal engine I would think keeping throttle position the same while going over the hill would be best.
     
  5. desdemona

    desdemona Well-Known Member

    Thanks-- can the Scan Gauge help you do this or no? Does the rpms tell you anything?

    I am not doing FAS, I wouldn't do NICE-on because if I don't do something right I hear a nasty noise. This sounds suspiciously like stripping gears and is about as pleasant as chalk on a chalk board?

    RL Drifter: I didn't mean steady acceleration but you got my drift anyway. :) Of course, it is clearly *not* steady acceleration or you would go gradually faster. Of course, I am thinking you will end up going slower and slower. So Hobbit it isn't really gradual acceleration even if that is what I actually said. Sorry to confuse. :)

    I didn't know about the VW bus thing. I never had one. (Surprise given my age and so on I suppose.)

    --des
     
  6. firenurse4

    firenurse4 Active Member

    I watch the throttle position (TP) with the scan gauge for taking hills.
     
  7. desdemona

    desdemona Well-Known Member

    I think we are online at the same time now. I don't see a chat thing here, but can you tell me a little bit more about how you do this. I am new to SG (1st day really) and hypermiling.

    --des

     
  8. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

    Desdemona, the "gauge" setting on your SGII has configurable readouts -- 4 in fact. If you press the button next to one of the readouts you will cycle through the different gauges available. One of them is TPS -- Throttle Position Sensor. That uses a range of numbers which differs from car to car. Mine reads 5 with no pressure at all up to something over 20 for wide open throttle (pedal to the metal!! :eek:). If you have that readout up you can pick a number and make sure it does not change to be sure that the pedal is always in the same position.

    I find that with most hills (unless they are very slight indeed) I have to add at least a little pressure to keep from dropping below a safe speed for the traffic. If you are all alone, just make sure you can get over the hill. ;)
     
  9. desdemona

    desdemona Well-Known Member

    This is very understandable (unlike my initial post :)). I even printed it out and am going to look at my SG for it.


    BTW, I know a certain teenager that uses 20 to back up out of the driveway!


    --des


     
  10. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

    Glad to help!!

    Just to be sure we are on the same page, this is the screen I was referring to:

    [​IMG]
    (Pulled from http://scangauge.com)

    I don't remember what mine defaulted to but you can change the readouts to whatever you like.

    Keep asking questions if you get confused! :thumbs_up:
     
  11. HAFNHAF

    HAFNHAF Well-Known Member

    there is also an engine load readout available as one of the gauges. i would think that would be the best thing to monitor in this case.
     
  12. benffv

    benffv Well-Known Member

    the only hills in Delaware are bridges. I have a choice of 2 going to work 1st bridge is 1mile to the top and 1mile to the bottom, coasting i either keep the speed or slightly slow down from winds. I can't coast good on that because of the high speed drivers drafting me even though their is 2 other lanes beside the slow lane. I only use this bridge coming home because i have to decel to take the exit ramp. the 2nd bridge is .5miles up .5 down, i use that all the time going to work i coast and speed jumps 7-9mph by the time im at the bottom, also the speed limit is 10mph less.
     
  13. desdemona

    desdemona Well-Known Member

    Hi.

    The screen shown has a rpm-- I thought you were talking about tps (throttle position).
    Though in a different post you talked about rpms. I wonder if you could use this in both
    DWL and P&G?? NICE-on and DWL seem to be very closely related things, and also I would not want
    to be changing displays while driving. I don't even change the radio while driving (except to hit a button).

    Someone mentioned Engine load, so boy there is a lot of info there!

    If so, I would like to know how that would work. This might be a crazy question. I don't know
    very much about all this.

    --des

     
  14. Right Lane Cruiser

    Right Lane Cruiser Penguin of Notagascar

    Des, the picture is just an example of what you can configure on the "Gauge" screen. I've got mine set up with TPS in the upper left corner, MPH in the upper right corner, VLT (Battery Voltage) in the lower right corner, and MPG (Instantaneous Fuel Consumption) in the lower left. When I want RPM, I just press the button to the right of the upper right corner to cycle through available readouts until I get to RPM. I often switch out the VLT reading for LOD (Engine Load) the same way.

    Just pick 4 readouts you'd like to monitor and go for it! The only thing it won't do is show your mpg for anything other than instantaneous. It would be great to be able to have instantaneous AND current trip mpg on the same screen but it won't let you do that (yet).

    Hope that gets you going!

    At a guess you might want MPG, TPS, LOD, and RPM on your display. Let us know how it goes, okay?
     
  15. SlowHands

    SlowHands Hypermiling Ironman

    I have my ScanGauge configured as: top left RPM, bottom left MPG, top right either LOD or GPH, bottom right TPS. To get to current MPG its 2 hits on the 'home' button, and then back to the gauges is 1 hit on the home and 1 hit on the 'gauges' button. Makes for minimal time with eyes not quite on road... although I do have my SG set on top of the dash so I can see it with almost no drop of my eyes from the road, its incorporated into my 'continuous visual sweep' of road, mirrors, gauges, surroundings...
     
  16. psyshack

    psyshack He who posts articles

    Let talk basic load driving and how it works with a hp/tq curve.

    This is not a dyno pull of my car. It is a 06 Mazda 3 hatchy 23.l. Same engine as my car. The hp/tq are wheel numbers not crank numbers. I would think the dyno run was more than likely made in 3rd gear. I feel this was either a very heavly weighted pull or there was a automatic transmission in the car.

    [​IMG]

    The torque curve is at the top. The horsepower is the diagonal. One reason I bought my car is it is known to have a flat torque curve as seen in this dyno run.

    So lets say Im pulling a hill at 2800 rpm. Find 2800 rpm at the bottom. Now look at the vertical line as it intersects the hp and then torque curves. Assuming that I am climbing a hill at 2800 rpm in third gear. In the car for this curve. I would be using about 63 hp and 118 ftlbs in torque. Now as the climb increase in length or steepness. My rpms might very well drop. So lets say they drop to 2200 rpm just as I crest the hill. Im holding the throttle steady and not giving it anymore gas. Im now down to 48 hp and 116 ftlbs of torque. With the drop of a few hundred rpm Ive lost speed and hp. But not hardly anything in torque.

    The torque will twist the bolt into. But the horsepower decieds how fast the bolt gets twisted.

    As I crest that hill and start down the backside. The amount of torque I have will stay the same within reason. But even with bleeding out of the throttle my avealible horsepower as the rpms rise becomes greater. And less fuel is used to tap that hp and tq.

    As your pulling the hill load goes up. As you crest the hill and bleed out of the throttle load goes down. The only thing that changes in this mess is the load that is represented to the motor by the car. Be it a hill, wind, rain, AC. Hp gets you up the hill faster at the cost of fuel. In my case Im already using 90% or better of the tq. More rpm gives me more hp and fuel use. But little in the gain in torque.

    psy
     
  17. desdemona

    desdemona Well-Known Member

    I did figure out how to configure the SG. Right now I have mpg, rpm, tps, and mph. I know this sounds redundant, but I like the digital mph vs the analog one that is on the car. I can tell if i am going tiny amts under the speed limit and so on. Also I have the SG almost as a heads up display which is kind of nice.

    I'm not quite sure exactly what the rpm per minute does for me at this stage. Not much I think, but I have tried using it to try and do P&G.

    --des
     

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