What is the continous speed of lowest consumption?

hey doc, glad to see u this am. got a silly question. i was under the impression that my "old" 04 prius could automatically lock the doors as i was driving. cant seem to do this with "mr red" without using the lock button. not a big deal but iwas just wondering.

 

For the older, NHW11 model, my data suggests it is 18 mph. This was also the average speed of the Insight marathon.

Bob Wilson

 

thanks, doc. thought so. btw, michael, i apologize for cutting into your post with my question. after i did that i realized i was pretty impolite. so please excuse me. the proper thing for me to have done was to pose my question under a new thread.

 

Sorry, I should have posted my MPG vs MPH graph:


You'll see a combination of a math model and actual mileage with my 2003 Prius. The NHW20 tends to do better but near as I can tell, shares many of the same characteristics.

Now if you are curious about an optimum highway speed, 65 mph seems to work best. At 70 mph, there is a decrease and at 75 mph, the NHW11 really hits a wall. The NHW20 has a little better high speed performance but we're not talking 'a miracle.'

There is a control law transition at 42 mph that both vehicles share. My experience has been that being 3-4 mph slower or 3-4 mph faster than 42 mph works great. But if you transit 42 mph often, the overall effect is worse fuel economy.

GOOD LUCK!
Bob Wilson

 

Can your model be used to predict the performance of pulse and glide?

 

With fixed and without fixed refers to load?

In other words, the blue line is P&G/Warp Stealth while the green line is cruise control (ish)? Or is the green line DWL type driving, not CC?

Looks like DWL or CC (as the case may be) is pretty good at highway speeds, with Warp Stealth applied based on terrain/exits rather than in level continuous driving for easy near-max FE?

 

I assume you're aware that pulse and gliding (P&G) is the most effective way to get high mileage. You accelerate to 40 mph, then glide (no arrows, do this on downhills if you can, to extend the glide distance), down to a speed that traffic & conditions allow, and repeat. Above 41 mph, the gliding mode changes and it's harder to do it without the engine on.

The American record for distance on a single tank (what was it, 1200 miles at 100+mpg) was done this way, pulse to 40, glide to 30. That's those black dots in the chart above that say "NHW20 marathon".

 

So, I see a lot of data points around 50mpg, between 45 and 65 mph. I would think the mpg would vary a lot more in that wide range of speeds.

 

The Prius has a certain amount of fixed, ~4-500 W, overhead to run the control computers, brakes, and day-light running lights. This is the "fixed" overhead. If we could eliminate it at low speeds, the performance would improve.

Bob Wilson

 

Yes and it has me curious too. My current hypothesis is we are in a higher engine efficiency range up to about 65 mph. The curve assumes a 31% ICE efficiency but Toyota reports up to 36-38% efficiency. This is very curious area.

What is known is once speeds exceed 65 mph, the NHW11, 2001-03 model year, Prius begins to take a performance hit. At 75 mph, it is in the toilet, 39 MPG and this is reproducible.

The NHW20, 2004-current, have somewhat better although not "magic" improvement at speeds of 75 mph and above:


Bob Wilson

 

The model, no, but I have 10 data points recorded at:

• cruise control 34 mph
• pulse and glide 25-42P&G (same average speeds as 34 mph)

One of the maddening things about the Pulse and Glide advocates is they never think to compare their P&G performance over the same route and conditions as cruise control at the same average speed. It is maddening because they make claims without comparing it to the exact same end-to-end performance over the same route at a constant speed.

My data suggests there is a slight improvement at 34 mph but not enough to change my driving habits to P&G over maintenance of a steady state speed, even using cruise control. The only exception is in cold weather warm-up, 1.5-2 miles, when I average a speed of 25 mph through the neighborhood while the engine continues to run. But after the Prius engine is warmed up, 70C coolant, my data has yet to find a P&G profile that is worth the effort.

Understand I have no problem with terrain driving, using the up and down grades, to optimize performance, which I find perfectly sensible. But to call terrain driving 'pulse and glide' . . . well that is playing semantic games. It means "pulse" up the hills and "glide" down the slopes . . . duhhhhh!

If pulse and glide is go great, try it versus the equivalent steady-state speed on a dry lake bed . . . especially maintaining the optimum, average speed. (Ok, I'll get off of my high horse now.)

Bob Wilson

 

One more comment on what I have found with regards to speed and mpg.

When I went to LA this summer, I drove at 80-82mph on I5. It is a long flat road. The mpg gauge was nearly flat at 43-44mpg. I ended up with about 44mpg for that trip. So, my 2007 can definately beat 40mpg at 80+ mph.

 

This is very interesting, and something I have been thinking about recently. My perception is that I get better mileage at ~40mph than I do at 30mph. At 30mph I don't seem to be going fast enough to "amortize" the fuel burned over enough distance to get over 50mpg. At ~40mph I find it pretty easy to back of the gas and cruise at 55-65mpg. Now, this is only perception based on real time mpg. In reality, if I had occasion to cruise longer distances at 30mph, it may very well average to a higher mpg if the car starts cycling between modes automatically and as I would spend less fuel getting up to speed. Surface street speed limits around here are 35-45, so everyone drives 40-50 so its hard to get to spend much time at 30mph w/o causing problems.

Can anyone comment on this phenomenon?

rob

 

Here is an interesting chart. I know I got it from this site, but I dont remember how it was derived.

 

I beg to differ. 65 MPH is a HUGE hit over 55 MPH, about 20%. In fact, just last night on my regular Monday long drive, I got gas 42 miles from my destination. Drove 55 MPH on CC and arrived with EXACTLY 60.0 MPG on the MFD. This was on I/91 in Vermont and northern MA. Hills and valleys, not desert flat. Stayed there 1 hour and started the return trip. I had to do 65 MPH in order to pick my daughter up from band practice on time. When I got to the exit where I had gotten gas, it was under 52 MPG on the MFD. Down to 47 by the time I got home.

Over MANY 'all controllable variables reproduced' trips on this 390 mile round trip I have seen MPG of 43 to 47 at 65 MPH and typical 55 MPH numbers of 53 to 57 with a few higher.

Drop (and enforce) the speed limit to 55 MPH and this country will save a LOT of imported oil. We don't need ethanol, we need fuel efficient vehicles and less "need for speed".