Instantaneous MPG readings for best fuel economy

Looks like a data logger would be useful. The SoC is going to make the results hard to repeat. Is the drive state of "deadbanding" the best for acceleration or should one take a little from the battery? and does MPG remain constant in this deadband as the speed increases?

This morning I used litres per hour and miles per litre alongside rpm and coolant temperature on the ScanGauge. Litres per hour was used as a measure of acceleration effort and miles per litre to fine tune the throttle when cruising (at around 50mph). These settings might be useful in comparing MPG and rpm. I am using litres because it gives me better resolution (and the US gallons are short measures).

 

<div class='quotetop'>QUOTE(JimboK @ Apr 30 2007, 03:57 AM) [snapback]432458[/snapback]</div>

As I am not going to multiply numbers in my head as i am accelerating from a red light... to even simplify further, could we state that if we kept the MPG figure approximately the same as MPH figure, we would be doing just fine?

That would be a great rule of thumb... very easy to follow and visualize.

 

Thanks for posting this. I have a dumb question; why would accelerating with MPG > 1.2MPH be a problem? I don't see the need for an upper limit. Or is that just the best you can typically achieve?

Since you posted this I have noticed yesterday and today that when I accelerate from a stop, my MPG is usually somewhat less than 0.5MPH until I get up to speed, even worse going up hill obviously. I haven't played around with acceleration techniques too much, but I generally try to get up to speed pretty quickly and smoothly without jackrabbiting or anything. I thought that was the most efficient method. Could I not be pushing it enough? When forced to go slower (if someone is in front of me), I have noticed that MPG is still usually less than 0.5 MPH. Once I start maintaining speeds around 45 - 60 MPH, MPG usually equals or exceeds MPH unless I'm going uphill, but then I get much higher MPG on the downhill glide/warp stealth. I think I really need to get a ScanGauge to start monitoring RPMs.

 

I see now. Thanks Jim. I'm going to play around some more with acceleration from a stop on the way home today and will let you know if I have any more luck getting MPG above 0.5 x MPH.

FWIW, I don't see the math problem with this rule as comparing your MPG readout to half your speed barely qualifies to me. I guess with the 1.2 x MPH it could be more problematic for some. But I would think that not letting MPG get too much above MPH would be sufficient for most.

 

<div class='quotetop'>QUOTE(Highly ImPriused @ May 1 2007, 09:10 AM) [snapback]433321[/snapback]</div>

Keeping the MPG equal to MPH is not rigid... just visually easy. In fact, even if not achievable, it would be just an easy objective to try to attain.

As a specific example, Highly ImPriused is now at 0.5 MPH... and you can see that he is trying to change / understand his acceleration behavior to move closer towards 1.0 MPH. Of course, if you can do better than 1.0 MPH then you might be better off... but it has diminishing returns and, for the general public, moving them towards 1.0 MPH would have a significant impact on MPG.

Another way to look at it is for the instruction to be: As you accelerate, try to keep the MPG number equal or close to the MPH number. If you go below half the MPH number, then you really need to improve.

 

So I tried some different ways of accelerating from a stop on my commute home yesterday and back in this morning. I found that in order to get MPG > 0.5 x MPH, I had to accelerate pretty gingerly. Much slower than what I had previously been led to believe was the most efficient way of accelerating, based on other posts on here. I never floored it before, just gave it what I considered to be decent acceleration; nothing that would throw your head back or anything. I had to go much slower to achieve this goal; certainly not slow enough to use just battery power, but not a whole lot more than that. I wonder if this is just me for some reason or if others are finding this to be the case as well. BTW, acceleration to maintain speed or increase it a little bit when already moving hasn't been a problem. I'm easily able to get MPG in Jim's target zone in those situations on a flat.

Regarding the upper limit of 1.2 x MPH, a situation came up a few times that had me questioning it again. Say you're traveling about 40 MPH and need to maintain speed due to traffic on a slight uphill where gliding is not possible. I've found that in these situations I'm only using a little bit of ICE power and getting MPG > 1.2 MPH (maybe about 60 MPG at 40 MPH). I understand that technically this isn't a very efficient way to use the ICE. The only way to get out of it (since gliding isn't an option going uphill) is to accelerate a bit more and I find that I can indeed get MPG close to MPH while gaining a bit of speed. I don't have a problem with this, but isn't doing that ultimately less efficient if you're getting lower MPG? Say you have this situation for 1 mile prior to the next downhill where you can glide. To get to that point you are obviously going to use more gas over that stretch if you average 60 MPG vs. 40 MPG. I realize that we aren't talking about much gas here; I calculate it as a difference of about 0.0083 gallons (or just a little over 1 ounce) for the hypothetical 1 mile stretch. I think I'm probably using more battery power in getting the higher MPG and maintaining speed, but in my situation I very rarely see the SOC drop below 4 bars anyway (it usually resides between 5 and 7). I have no problem regenerating adequate energy due to the need for multiple stops on a hilly commute. So for my situation, it seems to me that maintaining MPG > 1.2 MPH in these limited situations is more efficient over all but doesn't really make that much a difference. Am I missing anything?

 

I think your missing a Scangauge II to monitor your RPM. If your that serious about improving your MPG, invest in an instrument that will help you better than the MFD ever will.

Wayne

 

<div class='quotetop'>QUOTE(FireEngineer @ May 2 2007, 09:46 AM) [snapback]433883[/snapback]</div>

:lol: I hear you and I'm planning on it. Just have to convince the wife ...

 

I believe how much percent you drive without ICE, gliding percentage, is the key.
The attached picture is came from the famous 1400 mile marathon.
http://www.greenhybrid.com/discuss/showpos...mp;postcount=77
It shows...
Distance Traveled: 150.78 Km (93.7 mile)
Avg. FE with Engine On: 9.84 Km/L (23 mpg)
Avg. speed: 39 km/h (24 mph)
Percent Distance ICE On: 19% (81% gliding)
Fuel Consumed: 2.942 L (0.777 gallons)
Fuel economy: 51.25 km/L (120.56 mpg)

In this case, avg. speed and avg. engine on mpg is almost same, 24 mph vs 23 mpg.
Anyway, the data came from my SuperMID M-1.
http://priusdiy.fc2web.com/

Ken@Japan

 

I have just had my first full week with the ScanGauge and I too have found that my past acceleration has been "too fast". The engine starts to make some noticable sound after 2600rpm, so if you hear this change then you are outside and above the sweetspot. Keeping within the 1700 to 2300 range gives me an acceleration of just over 1mph per second on the flat. Is this a good description of moderate acceleration?

81% gliding is amazing.

 

<div class='quotetop'>QUOTE(KV55 @ May 3 2007, 07:42 AM) [snapback]434627[/snapback]</div>

Wow, 1 mph per second seems really slow to me. But I think that's about what I had to do to get MPG > 0.5 x MPH. So I think that's a good rule of thumb. I'll confirm later today. Looks like I need to recalibrate my driving habits.

I agree about how amazing that 81% gliding is. Unfortunately, I don't think I could ever learn to tolerate an average speed of 24 mph over 94 miles. I'd go batty after 15 minutes of that for sure. Kudos to you Ken for doing it.

 

Quite welcome. This is actually fun to me. Plus it's giving me all the more impetus to get a ScanGauge eventually.

Nearly 50% of my commute is in the mid-speed range you describe (secondary roads with 40 or 45 mph speed limits). I try to pulse and warp-stealth as much as possible and that has helped. I'm up to 50 MPG on my current tank so there is some progress I think (my first tank came out to 39 mpg). There is an alternate route that is longer distance but involves about 50% interstate driving. I need to give that a shot and see how it compares over all.

 

hmmmmmmmm i thought the efficency range for the engine is 1500 + rpm? 1500 rpm is RIGHT about 4 liters per hour (1.1 gallon?) and that's where you get the best "Bang torque" for your liquids of fuel in the combustion chamber while minimizing pumping losses (which is not as much as a miller cycle but its still there).

Once you go over 5 liters an hour (1650 rpm +), I notice the deminishing effects of movement vs gas sprayed starts to really notice, since friction is an enemy to us all, so 1700 rpm would be my (performance accel) while 2300 rpm would be my (redline).

all stats from Can-view so i use the engine for power, then shut off and coast! pulse and glide for the win! the car was MEANT to be driven this way and those who try to cruise for high MPG in the CITY are just WASTING THEIR TIME. Not only the engine is below the efficency spot but usually in that crusing state your not using all the engine power to cruise (some juice is brought back to the battery) so conversion losses galore!

When your on the highway however (50 mph>) then the engine usually is IN the sweet spot to maintain those crazy areodynamic winds... but hey nothing a fat truck can't save us all (94 mpg segment on drafting the whole 7 mile highway!)

although its just a pisser when your pulsing, and then when gliding the engine is idling... doh... must install ev mode but too lazzyyy

 

Extremely helpful post, extremely helpful discussion. Before this, the instantaneous mileage readout was useless to me as a guide to fuel economy during acceleration. Now its not.

I hope Toyota reads this and acts accordingly. If the approximate optimimum, for typical (on the flat) conditions is really so well defined in terms of RPM range, then Toyota ought to equip the car with a "sweet spot" light, similar in concept to the "shift lights" on some manual transmission cars I've had. A simple visual clue to help the interested driver optimize fuel economy -- three lights (revs low, revs right, revs high).

For those who never had one, the "shift light" would come on if you over-revved the engine, to prompt you to upshift. It was not always right -- if you were accelerating uphill you had to have the sense to ignore it -- but it was right enough that, as I recall, VW actually got a higher EPA MPG rating when they introduced it because they convinced the EPA that the light would result in more efficient average driving. The shift light was just a vaccum gauge, I think, but these days, shoot, put in a tilt sensor for uphill and downhill, make the care aware of when you are accelerating from stop or near stop, monitor the flows into and out of the battery, and you could with little effort make the light come on only and precisely when its supposed to. I don't really see a barrier to putting this in any modern automatic transmission car. Do any currently produced automatic transmission cars have anything like this? If not why not?

Hah, for every good or bad idea I've ever had, somebody else had it first. Apparently there's a bill to require something like this by 2014.

http://www.washingtonwatch.com/bills/show/...N_357.html#toc0

"Requires passenger automobiles and light trucks be equipped with fuel economy indicators and devices beginning with model year 2014."

Well, that could just mean the instantanous milage readout.

Oh for dumb. Toyota already has it in the works, as described here:

http://www.treehugger.com/files/2006/10/toyota_eco_drive.php

"Tokyo — TOYOTA MOTOR CORPORATION (TMC) announced today that, beginning in October, new Japanese-market vehicle models with automatic transmissions will be equipped with the Eco Drive Indicator, a feature meant to encourage environmentally considerate driving. This development—aimed at reducing CO2 emissions through increased fuel efficiency—is part of Toyota's efforts to combat global warming.

Based on a comprehensive determination that takes into consideration such factors as accelerator use, engine and transmission efficiency and speed and rate of acceleration, the Eco Drive Indicator, located on the instrument panel, lights up when the vehicle is being operated in a fuel-efficient manner. This is hoped will raise driver awareness toward environmentally considerate driving and contribute to fuel economy."

HEY TOYOTA, BRING IT OVER HERE PLEASE.

The text description from Toyota makes it sound like what I was describing, but the article describes it as being a knockoff on the five-minute bars in the Prius.