The correlate RPM, speed, MPG, etc thread mentioned low-load driving and I found myself once again thinking: how do you do that? I have a ScanGauge 2 and usually see LOD around 75-80 on the freeway between 1600 and 1800 rpm. This generally translates to anywhere from 50 to 65 MPG at 60-65mph. A few times I have gotten into some weird mode where I can see sub-70 LOD at 1700 rpm by pushing the car past 4500 rpm and then pulling it back, but at these points economy is worse, between 40 and 50 MPG. I find that this state is stable until I take my foot off the gas and ease it back. I would've guessed the sub-70 was the low load situation, but then I was eating more gas. So it is I am utterly confused and hoping someone can help me dig myself out of my 53 rut.
<div class='quotetop'>QUOTE(zqfmbg @ Jul 9 2007, 02:01 AM) [snapback]475375[/snapback]</div> Some of us need to know where the OBDC II port is located and what it looks like. Any assistance is appreciated.
<div class='quotetop'>QUOTE(zqfmbg @ Jul 9 2007, 03:01 PM) [snapback]475375[/snapback]</div> I don't understand what you mean "low load", but Prius is trying to power against the certain wind resistance and we need more fuel to drive faster. I mean lower mpg at higher speed or higher mpg at slower speed. http://priuschat.com/index.php?showtopic=15285&st=32# Ken@Japan
<div class='quotetop'>QUOTE(JimN @ Jul 9 2007, 09:56 PM) [snapback]475887[/snapback]</div> It is right next to the steering column. If you get your head (or a mirror) down of the floor in front of the drivers seat, it is there right up against the dashboard to the right of the steering column. You just shove the ScanGauge or whatever device connector vertically up into it. It has no cover or anything. The main hassle is routing and securing the extra cable.
Ahh, I think I finally understand the question. Here's what I think is the answer: The beauty of HSD is that it always tries to keep the engine working in its most efficient state, which is at a relatively wide throttle position. This translates to that 70-80% load that you see on the ScanGauge. To increase power it spins the engine faster, to reduce power it forces the engine to spin slower while keeping the throttle cracked fairly wide. This reduces pumping losses against the throttle plate and keeps system efficiency nice and high. You want to see the the load in that range while you are using the engine because that's how you get the most useful energy out of your fuel. Lower load means that the system has fallen out of that high-efficiency mode, usually because power demand is unusually low. Flat-road cruising below 45mph or so will do it. Instant fuel economy reads high but ultimately you aren't getting as much out of your precious milliliters of gasoline. Here's how I've put that to use: My commute is on 50-60mph roads with gentle, rolling hills. If I set the cruise control the engine would bounce back and forth between wide throttle, efficient running and closed throttle, low-load running. Pretty much anything below 1500-1600RPM is bad. So I use terrain and subtle changes in speed (plus or minus 3mph at most) to keep the engine in the "good" zone. I try to plan it so that I have a little extra speed when the engine is entering the low-load "bad" zone (like coming down the back of a hill) so that I can back off of the accelerator for a period of "warp stealth" which doesn't burn any fuel. (Arrow from battery to wheels only, ICE spinning but not burning. No arrows is possible and preferable but very, very touchy to maintain near the top of the accelerator's travel.) Once I reach the bottom or hit my -3mph lower limit, I re-apply the accelerator and jump right back into the high-load zone abouve ~1500RPM. Rinse and repeat. That gets me a very consistent 60mpg @ 60mph, better when I don't have to use the A/C. Too much information?
<div class='quotetop'>QUOTE(zqfmbg @ Jul 12 2007, 11:34 AM) [snapback]477279[/snapback]</div> You're welcome! Our understanding is that Prius requires a lot of energy just to spin the ICE above the 42 mph barrier. We believe there is no magic at highway speed, but slower is better. However, there are a lot of potential to improve the fuel efficiency below 42 mph. http://www.cleanmpg.com/forums/articles/t-...-2006-1793.html Ken@Japan
<div class='quotetop'>QUOTE(zqfmbg @ Jul 9 2007, 01:01 AM) [snapback]475375[/snapback]</div> I have a ScanGauge and I have never seen a 70 load in the conditions you mention. Are you driving all uphill or constant headwind? My load typically stays under 60 on the highway at speeds under 70MPH. I can obtain 65MPG betwen 63-67MPH keeping RPM between 1450-1650 and load never see's 60. Wayne
<div class='quotetop'>QUOTE(FireEngineer @ Jul 12 2007, 09:38 AM) [snapback]477492[/snapback]</div> What is your technique for doing this? I've seen the 63@63 figure in one of hobbit's things but haven't seen an explanation of what people are actually doing. P&ws between 63 and 67? Or ice-on all the time and varying rpm?
<div class='quotetop'>QUOTE(FireEngineer @ Jul 12 2007, 10:38 AM) [snapback]477492[/snapback]</div> This is interesting. Wayne, my observations are similar to yours. Brick and I had some dialog (starts at post #14 in the thread) a while back in CleanMPG about similar differences. He speculated something could have changed between model years. Your car and mine are 2005s, whereas Brick has a 2007 and Zqfmbg a ???. (Zqfmbg, it would help others help you if you'd add vehicle details to your profile.) Whatcha think?
<div class='quotetop'>QUOTE(douglas001001 @ Jul 12 2007, 09:53 AM) [snapback]477497[/snapback]</div> ICE on all the time. Come out to an event/meeting one day and I'll show you . <div class='quotetop'>QUOTE(JimboK @ Jul 12 2007, 10:42 AM) [snapback]477522[/snapback]</div> Jim, I can't imagine that huge a difference between an '05 and an '07. If so, we should be seeing a big difference in MPG average between all early vs. later Prius. We're pulling 70+MPG but then so is diamondlarry so I don't think it is the car software. Sounds like an experiment at Hybridfest, let's get the Scangauge out and drive some different model years and find out. Wayne
<div class='quotetop'>QUOTE(FireEngineer @ Jul 12 2007, 11:56 AM) [snapback]477529[/snapback]</div> Works for me. I too can't see any reason for -- or evidence of -- a change in vehicle function. Agreed, our results are too similar. Perhaps just a minor change in how LOD is calculated?
I know diamondlarry will be there. If we could just get brick and his "loaded" Prius out as well. Wayne
Folks, I don't know if this is of any help, but I have access to 2 2007 Prius (company cars) in addition to the one I drive (also a company car) and I don't recall ever seeing an LOD value much greater than 60. The values I see are typically between 35 and 55 or so. Something is amiss here. I am using scangauge II's as well. MSantos
I recently made a trip from Elkhart, IN to Cedar Point in Sandusky, OH.(435.5 miles) From the time I left home until the time I got back and filled up, I averaged 64.9 mpg calculated. I started out by going up to 60 mph and bleeding off speed down to 54. I accelerated to 60 using a TPS of 27 and bled speed at a TPS of 19. A little over halfway there I switched to 55-49. I didn't think to pay attention to the LOD even though that was one of the guages I was monitoring on the SG. I think that the acceleration phase was at ~85% though. I try to remember to look on my way to HF to see what the steady state cruise level is.
That strange state from revving above 4500 and slowly pulling back has been discussed a little over in prius_technical_stuff, as something I for total lack of a better term call "WFO mode". [WFO is a cruder form of WOT.] The throttle definitely opens *more*, so I'm at a loss how you saw *lower* loads. This is when my vacuum gauge pegs at zero, not 4-5 in-Hg like normal. And as you noticed, MPG totally tanks. I managed to hold this state for several longish stretches on highways and even got the cruise control to be able to hold it once, but those segments were always lower so I figured it was a sort of special "screaming power" mode used only when you really really need it. Why the different running parameters persist on a gentle backoff [until you drop below about 10 kW demand, if I remember right] I can't imagine. Another designed-in mode, like warp stealth, but less useful to most of us. . The "%load" figure during most highway driving seems to weigh in for most people around 50%. I think your OBDII widget has some issues. . _H*
<div class='quotetop'>QUOTE(JimboK @ Jul 12 2007, 11:42 AM) [snapback]477522[/snapback]</div> Ahh, yes. I remember when this came up before. I haven't been using my ScanGauge much but this makes me want to break it out again to have a look. For the last few months I've just kept an eye on the analog tach to keep the engine above 1,500RPM and preferably not much above 2,000RPM if I can get away with it.
I can't seem to figure out how to do multiquote replies, so I'll just handle everything at one here, I guess. I'm driving a stock 2007 (stock tire pressures, no foam, no block heater, etc) with a ScanGauge 2 I've had for a few months now. I consistently see these LOD numbers: 25 when idling 50 in stage 3a (I think that's right) and coasting 70-80 at cruise 80-90 when accelerating Might've messed up something in setup, but I think everything's correct (1.5L engine, hybrid, etc). I haven't properly calibrated fuel consumption on it yet. Today, the air temperature on my commute was just around the 80s (BTW, has anyone else seen the MFD air temperature readout being really slow to increase?) and I was easily managing 60+ at between 60 and 65 mph, 1600 RPM, and the aforementioned 75 LOD. So I guess it's still enigmatic and I still don't know quite what I'm doing.
<div class='quotetop'>QUOTE(zqfmbg @ Jul 13 2007, 06:20 PM) [snapback]478383[/snapback]</div> Still can't explain the discrepancy between your LOD readings and those of some of the rest of us, but I can help you with this. Click the "Quote" button at the bottom of each post that you want to quote. Then when you click "Add Reply" at the bottom of the thread, all will appear in the reply box.
