Pulse and Glide

sounds like your pulse is someones elses "tromping".

 

You're not seeing this correctly.. It all averages out, and it's distance traveled, not the time that is used for the average (if it were time, all you would have to do is sit at a stop light with the engine off and watch the average increase to infinity)..

Because it's actually measuring fuel consumption per distance traveled, it's exactly the same thing if you get a constant 50 MPG and travel one mile or pulse for an appropriate amount and glide the rest of the way using no more fuel; you've still travelled the same distance and used the same amount of fuel.. Obviously your velocity profile will be different, with the constant consumption generally producing a constant velocity vs. the pulse-n-glide creating a higher peak velocity that slowly falls off, but that's immaterial to the fuel consumption calculation..

Some people who have very good foot control and are more tuned-in to the behaviour of the vehicle can get very good mileage at a more-or-less constant consumption rate, others use pulse-n-glide to achieve the same thing.. Personally, I can't stand the pulse driving technique and the technique I use is a targeted consumption- ie, I choose an arbitrary consumption number, eg 50 MPG, that I want to try to maintain. I ignore the acceleration phase, but once I reach cruising speed, I feather the gas to try to achieve 50 MPG while maintaining my speed. I'll accept about a +/- 2 MPH and +/- 2 MPG variation, but I try to keep everything as steady as possible. Obviously, choosing a realistic target is crucial to the success of this technique, but 50 MPG is very much achievable and it is much less stressful than the constant pulsing..

 

If you calculate your mpg when you fill up, isn't it close to the MFD number...I'm only on my 3rd tank, but miles traveled and gas used bring my calculated mpg about 1 point apart.

terri

 

<div class='quotetop'>QUOTE(c4 @ Sep 12 2006, 09:27 AM) [snapback]318273[/snapback]</div>

or ... distance = 'rate' times 'time', whereas MPG = mile divided by gallons

 

<div class='quotetop'>QUOTE(Soylent @ Sep 12 2006, 09:21 AM) [snapback]318248[/snapback]</div>

I trust that any engineer employed at Toyota will know to average the MPG over gallons or fuel used, not over time or distance traveled. The pulse and glide benefit is real, evidenced by full tanks consumed using the technique.

On the other hand, we can fool ourselves by using the 5 minute time interval averages incorrectly. Suppose that I took your Prius out for a 25 minute spin and brought it back to you with the consumption screen showing 24 mpg for the first 5 minutes and 100 mpg (or more) for the next four 5-minute intervals. (The first 5 minutes' MPG is often low from warming up the engine.) Did I achieve a good average mpg on the 25 minute drive? Can we take the average of 24, 100, 100, 100, 100 and say that I achieved at least 424/5 = 84.8 mpg?

Scenario 1:
I drove an average of 72 mph for the first 5 minutes, traveling 6 miles and consuming a quarter gallon of gasoline. Over the next twenty minutes I travel at an average speed of 12 miles per hour, traveling 4 more miles, consuming 0.04 gallons of gasoline. Overall, I traveled 10 miles on 0.29 gallons of gasoline, averaging just 34 mpg.

Scenario 2:
I averaged 30 mph over each of the 5 minute intervals. In the first 5 minutes, I traveled 2.5 miles and consumed 0.104 gallons. In the next twenty minutes, I traveled 10 miles and consumed another 0.1 gallons. Overall I traveled 12.5 miles on 0.204 gallons averaging 61 mpg.

Scenario 3:
In the first 5 minutes I traveled 1 mile (averaging 12 mph) and consumed 0.04 gallons. Over the next 20 minutes I traveled 12 miles (averaging 36 mph) and consumed 0.12 gallon. Overall, I averaged 81 mpg.

We can't say what mpg was achieved by looking at the mpg over time graph on the consumption screen. Fortunately the car's computer calculates the mpg correctly.

(These three scenarios are purely hypothetical and only intended to show how the mpg over time chart can be misinterpreted, not to recommend any driving strategy for low fuel consumption.)

 

<div class='quotetop'>QUOTE(Soylent @ Sep 12 2006, 11:50 AM) [snapback]318348[/snapback]</div>

I feel that P&G is well worth the practice...it is now becoming automatic for me and I am only on my third tank...also, I use electric only as well...my car "wants" to go into this mode at very low speeds with some curves and hills...and stays in it for some time...I let it since I am going 15 mph...I can also glide in the 20 mph range, not just in the 30-40 mph range....

For me it's fun...but I have a big improvement over my first tank and I do all very short trips with lots of hills, bunching errands.

terri

 

Using the OP's original scenario, accelerating for 20 seconds, coasting for 2 minutes, and assuming a steady rate of acceleration and a different steady rate of deceleration:


The pulse takes you from 35MPH to 45MPH in 20 seconds, with a shown average the entire time of 10MPG. This would imply that your acceleration is 0.5 MPHPS. we could use calculus to determine the exact distance traveled, but since it's been 3.5 years since i've done any of that, we're going to go with the simple (and decently accurate) estimate of 40MPH*20s = 0.22 miles, at 10MPG, resulting in 0.022 gallons of gas consumed

For the glide portion, we assume a linear decrease in speed back to 35MPH over the next 2 minutes. Using the same estimation, we get a distance travelled of 40MPH*2m = 1.33 miles.

This gives us a total of 1.55 miles travelled and 0.022 gallons consumed, resulting in an average of 70.45 MPG for the entire distance, which, at these speeds, is about right for those out there with the really great mileage. Personally, i don't get this high too often, as i have too much traffic and too many stops to deal with in my commute.

note to self: update mileage number on green hybrid when you get home :-p been a number of tanks...

 

103 mpg for 47.8 miles round trip using pulse and glide

--------------------------------------------------------------------------------

Started at 508.9 miles 75 MPG on display, 6.785 gallons used since last fill, round trip segment to 556.7 miles 76.8 MPG , 7.248 gallons used since last fill. 47.8 miles for segment .463 gallons used, 103 mpg

trip od MPG--gal--miles--gal---MPG
--------disp--s/fill---------seg---seg
508.9 75.0 6.785
532.8 75.9 7.019 23.9 0.234 101.949
556.7 76.8 7.248 47.8 0.463 103.158

Pulse and glide does work, but it is not for everyone! My wife thinks I'm nuts.

Dennis
links to photos below

75.0 mpg at 508.9 mi start of segment

75.9 mpg at 532.8 middle of segment (turn around point)

76.8 mpg at 556.7 end segment (returned to starting point)

 

<div class='quotetop'>QUOTE(maineprius947 @ Sep 12 2006, 11:37 AM) [snapback]318408[/snapback]</div>

 

mpg on mfd= miles driven/volume gas injected into engine converted to gallons

pulse and glide doesn't fool anything.

 

nice tank maine

 

Thanks Dave and pcflorida. Note that I did not get 103 mpg for a whole tank only for 47.8 miles, my best tank is 77, see my precious prius over at greenhybrid to see some really amazing tanks by Carl H this summer. His average since May is between 83 and 84 MPG, truely amazing.

Dennis

 

<div class='quotetop'>QUOTE(Soylent @ Sep 12 2006, 08:21 AM) [snapback]318248[/snapback]</div>

It isn't going to artificially inflate the MPG. Miles per gallon is miles per gallon. The average miles per gallon is over time - it doesn't matter if you P&Ging or had your foot on the floor. The computer will divide the number of miles you have covered by the amount of fuel used since you last reset it and that will be your average MPG. Doesn't matter if you burn x gallons in 3 minutes or 3 days.

The five minute interval bars are just there for the convenience of seeing recent history. Each five minute bar is caluclated by the same computer that is measuring the average.

The computer smarts in this car controls the operation of three motors to meet drivng needs at any given time, measures fuel delivery in grams and monitors the health of everything... you really think that P&Ging will confuse it?

 

<div class='quotetop'>QUOTE(Soylent @ Sep 12 2006, 08:50 AM) [snapback]318348[/snapback]</div>

I wish more people would use there cruise control

 

I have always been a big fan of cruise control... until now.

Have just started driving without out it... and while it is more work, I am seeing an improvement in mileage. Here , we have lots of very minor changes in grade which can have a big impact on mileage- with the foot, can glide longer and have actually been able to glide uphill!

For some driving, like the NJ turnpike in traffic- I think there is probably nothing better than cruise..... just go with the flow and have a blast!

 

I drove with cruse control for about the first year on my car. The main reason I did not do pulse and glide from the get-go was that I have 2 numb feet from back problems. I did not think that I had the necessary sensation to do pulse and glide. August of 05 4 people in Pittsburg inspired me to give it a try. They got 110 mpg on one tank! So I started working on pulse and glide and now it is becoming automatic. I have gone from the low to mid 50 mpg to 5 months above 60 mpg and one tank above 70! If I can do it anyone can. I will not be getting 60 mpg/ month soon as winter arrives but I will do better than last winter.

 

great improvement Henry!! but i think you still have to look at the break in being part of that improvement as well. i am breaking in a new Prius and my mileage has dropped about 8 mpg and im in the best of parallel tests you can do. same driver, same basic routes, same driving technique. went from averaging 60+ mpg in the summer to struggling to get 53. whats worse, just saw article in paper that most of the country is going to winter formula gas today (sept 15) there goes another 5-8% lower mileage...


just had my first fillup on my Prius Part Deux and now i know why there is 3 asterisks around the

***Full Tank of Gas***

i think it means "your fullness may vary"

computer mileage 53.3
pump mileage......44.4

oh well, next year when the LT difference is less than ½ mpg and my average is up 4 mpg, the pain will begin to fade