Pulse and Glide technique: What SOC gives best fuel economy?

theorist · Jul 10, 2006

Hello. I have a question for all you hypermilers out there.

What state of charge (SOC) gives you the best results when using a pulse and glide technique. I'm referring to standard or low speed pulse and glide between roughly 30 and 40 mph.

If this question seems odd, here's the origin. I noticed that if the SOC is low, the system tends to want to charge the battery. At these times, I must accelerate more aggressively in order to deadband or approximate a zero or neutral current flow to and from the battery. The engine (ICE) operates at a higher load or apparently more open throttle, higher RPMs, and higher gasoline flow. Conversely, when I try to accelerate in the no charge or discharge deadband when the battey SOC is high, the engine seems to want to discharge more, and I must use longer, more gentle pulses of acceleration. The engine then seems to be operating at a light load, less open throttle, lower revs, and lower fuel flow. It seems that when using pulse and glide for long distances, if you're staying close to the no charge or discharge deadband, the engine load is closely connected to the SOC.

Unfortunately, I don't have CanView. I've read the excellent translations between the MFD's SOC display and the true SOC%. Thank you. I'm only approximating fuel flow indirectly through the MFD's instantaneous MPG. I'm only guessing at ICE rpm's and load from sound and feel. If you feel more comfortable talking in terms of most efficient RPM or Gallons/Minute, perhaps others can try to translate that into SOC for those of us without CanView.

I imagine that the ideal engine load or SOC depends on many things, including trip duration, terrain, and temperature. If it helps to focus the discussion, we could focus primarily on 15-30 mile trips on flat terrain, with very few stops, at 60 degrees F.

Thank you. I'd be delighted with our decision to buy a Prius for the excellence of the owner community and PriusChat even if I didn't love the car itself. You are amazing.

FreshAirGuy · Jul 10, 2006

<div class='quotetop'>QUOTE(theorist @ Jul 10 2006, 10:52 AM) [snapback]283781[/snapback]</div>

Hello. I have a question for all you hypermilers out there.

What state of charge (SOC) gives you the best results when using a pulse and glide technique. I'm referring to standard or low speed pulse and glide between roughly 30 and 40 mph.

If this question seems odd, here's the origin. I noticed that if the SOC is low, the system tends to want to charge the battery. At these times, I must accelerate more aggressively in order to deadband or approximate a zero or neutral current flow to and from the battery. The engine (ICE) operates at a higher load or apparently more open throttle, higher RPMs, and higher gasoline flow. Conversely, when I try to accelerate in the no charge or discharge deadband when the battey SOC is high, the engine seems to want to discharge more, and I must use longer, more gentle pulses of acceleration. The engine then seems to be operating at a light load, less open throttle, lower revs, and lower fuel flow. It seems that when using pulse and glide for long distances, if you're staying close to the no charge or discharge deadband, the engine load is closely connected to the SOC.

Unfortunately, I don't have CanView. I've read the excellent translations between the MFD's SOC display and the true SOC%. Thank you. I'm only approximating fuel flow indirectly through the MFD's instantaneous MPG. I'm only guessing at ICE rpm's and load from sound and feel. If you feel more comfortable talking in terms of most efficient RPM or Gallons/Minute, perhaps others can try to translate that into SOC for those of us without CanView.

I imagine that the ideal engine load or SOC depends on many things, including trip duration, terrain, and temperature. If it helps to focus the discussion, we could focus primarily on 15-30 mile trips on flat terrain, with very few stops, at 60 degrees F.

Thank you. I'd be delighted with our decision to buy a Prius for the excellence of the owner community and PriusChat even if I didn't love the car itself. You are amazing.
[/b]
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Theorist, you have offered contnuing evidence to support the addage that there is in theory no difference between theory and practice but that in practice there is. "Why don't I get the EPA Mileage?" by efusco is a good place to start.

If you search for pulse and glide here on Priuschat you will find many more theories to explain what is quite clearly the art of Prius driving.

berylrb · Jul 10, 2006

<div class='quotetop'>QUOTE(theorist @ Jul 10 2006, 08:52 AM) [snapback]283781[/snapback]</div>

What state of charge (SOC) gives you the best results when using a pulse and glide technique. I'm referring to standard or low speed pulse and glide between roughly 30 and 40 mph.
... I imagine that the ideal engine load or SOC depends on many things, including trip duration, terrain, and temperature. If it helps to focus the discussion, we could focus primarily on 15-30 mile trips on flat terrain, with very few stops, at 60 degrees F.
[/b]
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Excellent Question Theorist!

I thought I'd restate the main parameters of what exactly your question was Theorist, so that folks can focus on giving a direct answer to an awesome question! <_<

It has been awhile, but I've read those other posts in their entireity FreshAirGuy, I could be wrong, but I don't think they answered this question directly, in my non-tech speak, "How many green/purple bars to maximize mpg using the pulse and glide technique?"

This could be another keeper thread!

b

hobbit · Jul 10, 2006

Short answer: none. It doesn't matter. As you P&G normally, the
SOC will work itself back toward 60% and completely adapt to whatever
you're doing. Don't pay attention to SOC or "deadbanding", pay
attention to engine RPM [yes, you should get and install a tach]
and try to keep it between 1500 - 2400 for pulses, which makes the
engine work [efficient] but avoids high-power regions.
.
If you draw the pack down just a little for a longer glide and then
recharge on your next pulse, that's okay since it's minimal extra
energy conversion but definitely helps you keep your *speed* more
evened out -- less confusing for drivers behind you. It is way more
important to concentrate on your environment and be safe, rather
than trying to drive like a nutball trying to match some little
arbitrary number you think your car's telling you.
.
_H*

TonyPSchaefer · Jul 10, 2006

Hobbit's correct, of course.

However, I tend to use the battery too much and stealth more than I should on occassions. I agree with Theorist in that when the SOC is low, the MPG is very low. Frustratingly so. This is further proof that using the EV button will hurt your mileage.

On the other hand, when I can use the EV and keep the SOC above half then I don't mind or notice a hit in performance. This is why I say that I try to use the EV button very judiciously.

But getting back to the topic, I think P&G is easier when the SOC is high, like Hobbit said, and the engine will focus on recharging the battery when SOC is low, like Theorist said.

tomdeimos · Jul 10, 2006

My car seems to automatically keep the battery charge in the range 54 to 63% about 90% of the time.
My main goal in slow driving is to keep the engine going on uphill runs and off for down hill.

If I don't work at this and just drive I find I am often going up hills using lots of bettery power, or running the engine while coasting down hills or stopped at lights.

Left to itself the Prius seems to try to cycle the battery up and down in the range almost independent of terrain.

efusco · Jul 10, 2006

I want to reiterate a key point Hobbit mentioned but could be lost. The OP seems to be under the impression that the pulse portion of P&G should be done with a 'dead-band' technique--no arrows to/from the battery.

That is exactly wrong. The whole purpose of the pulse portion is to recharge the battery. Thus it's necessary that arrows go toward the battery on the energy display. Thus Hobbit's recommended RPM range. I actually use fuel flow rate with CAN-View, but suspect doing so keeps me well within the RPM range he recommends.

Gliding with High SOC is easier. You can 'goose' the accelerator a little more when SOC is high to get you up and over little rises. When the SOC has dropped to the 50% or less range even the slightest pressure will force the ICE on to preserve the battery and provide the power you need.

I'd say that most of my P&G time keeps the SOC b/w 51-56%...3-5 blue bars on the Energy screen.

kDB · Jul 10, 2006

<div class='quotetop'>QUOTE(efusco @ Jul 10 2006, 02:11 PM) [snapback]283981[/snapback]</div>

... The whole purpose of the pulse portion is to recharge the battery...
[/b]
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i agree, you have all this stuff draining the battery (ac, stereo, etc...), so you need someway of recharging it. obviously when using P&G your not getting any brake regen, so it has to come from the ICE.

best thing to do would be install a tach and go by that. if not, then just try to keep it at around the same MPG range, say 25MPG at 35MPH. then let the car decide what to do with the energy. try to keep the accelerator at the same point through the pulse. so you would start at say 30MPH with 21MPG, then hit 40MPH at 28MPG.

P&G is more about the glide than the pulse. so keep the SOC up so the car will quickly shut off the ICE when gliding.

ken1784 · Jul 11, 2006

Let me explain how Japanese mileage enthusiasts are talking about...
There are basiccally two parties, one is keeping the battery level 6 and the other is using the wide range of the battery level, 4 to 6.
Both parties achive very good mileage results. The difference between them is the average speed, the level 6 party drives higher than the wide range party.
At low speed, it is more efficient to drive by motor the ICE, so the wide range party is using a lot of motor power to the level 4.
At high speed (below 42mph this case), it is more efficient to use the ICE power, then this party keeps the level 6.

Anyway, the key to improve mileage number is how long we can glide.
My SuperMID M-1 can display the ICE drive distance percent.
Please refer to the attached pictures and find the the ICE drive distance percent number in the middle of last line.

Photo-A: the best round of 1400 mile marathon
39km/h(24mph), 51.25km/L(120.6mpg), 9.84km/L(23.1mpg) ICE only mileage, 19% ICE distance

Photo-B: Some Japanese commute result at low avg speed in a lot of traffic.
27km/h(17mph), 40.16km/L(94.5mpg), 7.62km/L(17.9mog) ICE only mileage, 19% ICE distance

Ken@Japan

VABeachPrius · Jul 11, 2006

efusco,

I am mistaken too. I was under the impression that the pulse portion should be done with no arrows to or from the battery. To reiterate what you said; the yellow arrow to the battery should be present while pulsing from lets say 30 mph to 41 mph?

Thanks,

Chris

efusco · Jul 11, 2006

<div class='quotetop'>QUOTE(VABeachPrius @ Jul 11 2006, 07:11 AM) [snapback]284359[/snapback]</div>

efusco,

I am mistaken too. I was under the impression that the pulse portion should be done with no arrows to or from the battery. To reiterate what you said; the yellow arrow to the battery should be present while pulsing from lets say 30 mph to 41 mph?

Thanks,

Chris [/b]
Click to expand...

Correct.

The confusion may come from the discussions about 'dead-banding' (no arrows to/from battery) being, theoretically, the most fuel efficient way to accelerate. But once you start looking at the overall pulse/glide procedure one must recharge the battery somehow and it makes most sense to do that during the 'pulse' portion of the technique.

VABeachPrius · Jul 11, 2006

efusco,

Thank you for the response. Section 8, from your great document states the following:

8)Speed, braking, acceleration, and anticipatory driving--The MFD's Energy and Consumption screens present a degree of feedback unprecedented in any other stock vehicle. It acutely increases our awareness of what is happening from moment to moment, every 5 minutes, and over time.
This has affected the way I drive dramatically and many other Prius drivers notice the same. I accelerate fairly briskly getting to speed. I don't floor it, but maybe depress the pedal 1/3rd way or so. Once I get over the 25-30mph mark I begin trying to 'Dead-band'--on the energy screen all power is from Engine (ICE) to wheels with no arrows to or from the battery. This is the most efficient power phase as there are no losses from converting the energy to potential energy in the battery back to kinetic energy for the wheels.

Have you found that even though dead-banding may be the most efficient use of the engine that your overall mileage has increased from accelerating while there is yellow arrow flow to the battery during the pulse?

Thanks,

Chris

efusco · Jul 11, 2006

I no longer routinely try to dead-band. My FE may suffer slightly, I suspect it's too small a difference to measure or to know with certainty. But the brisk acceleration is more traffic friendly.

edeng · Jul 15, 2006

Hi everyone,
As a newbee I'm open to any and all advice on getting the best perfromance from my Prius. Love it! Fun car!
After searching "Pulse & Glide" and reading lots of the messages I still don't know what "Pulse & Glide" means and how do you do it to achieve better mileage. Many messages also use other acronyms which are confusing and not helpful.
I only have about 250 miles on my Prius and my typical driving is just 7-10 miles, twice a day, fairly flat, low traffic, local roads, mostly 45- 55 miles per hour. Overall average is only 44.5 miles per gal. Very little air conditioning so far. Once up to 35 mph most instantaneous mpg readings range from 40's to 50's to 60's and above. Fun to watch, but why is overall average not 50 or higher?
Are there some basic references to "Pulse and Glide" or other driving techniques anyone can refer me to?
Thanks in advance.

hdrygas · Jul 15, 2006

<div class='quotetop'>QUOTE(edeng @ Jul 15 2006, 02:14 PM) [snapback]286894[/snapback]</div>

Hi everyone,
As a newbee I'm open to any and all advice on getting the best perfromance from my Prius. Love it! Fun car!
After searching "Pulse & Glide" and reading lots of the messages I still don't know what "Pulse & Glide" means and how do you do it to achieve better mileage. Many messages also use other acronyms which are confusing and not helpful.
I only have about 250 miles on my Prius and my typical driving is just 7-10 miles, twice a day, fairly flat, low traffic, local roads, mostly 45- 55 miles per hour. Overall average is only 44.5 miles per gal. Very little air conditioning so far. Once up to 35 mph most instantaneous mpg readings range from 40's to 50's to 60's and above. Fun to watch, but why is overall average not 50 or higher?
Are there some basic references to "Pulse and Glide" or other driving techniques anyone can refer me to?
Thanks in advance.
[/b]
Click to expand...

I had a similar route to and from work. I now take a parallel route that is a bit more hilly up and down but all below 40 mph and I am now getting >10mpg better. I am a believer in the break in period. You need a few more miles on the car. Look at the basic better MPG sticky. Tire pressure is key. P&G is important but between 45-55 is a no go. After a year of really working on my P&G I can mostly do it by feel but that takes time. Start now and practice.

ken1784 · Jul 16, 2006

<div class='quotetop'>QUOTE(edeng @ Jul 16 2006, 06:14 AM) [snapback]286894[/snapback]</div>

I only have about 250 miles on my Prius and my typical driving is just 7-10 miles,[/b]
Click to expand...

The reason of your low mpg is such short trips.

Look at the consumption screen when you finished driving.
It is something like...
1st 5min: 30 mpg
2nd 2min: 45 mpg
3rd 5min: 55 mpg
Then, the average is about 45 mpg.
The low mpg number in the 1st 5min is caused by engine warming up fuel usage.

Ken@Japan

theorist · Jul 16, 2006

<div class='quotetop'>QUOTE(ken1784 @ Jul 16 2006, 01:42 AM) [snapback]287061[/snapback]</div>

The reason of your low mpg is such short trips.

Look at the consumption screen when you finished driving.
It is something like...
1st 5min: 30 mpg
2nd 2min: 45 mpg
3rd 5min: 55 mpg
Then, the average is about 45 mpg.
The low mpg number in the 1st 5min is caused by engine warming up fuel usage.

Ken@Japan
[/b]
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Your numbers point out that another factor is at play. The mpg over different time trips or time segments is weighted by the gallons of gas used rather than the time. Suppose that I start off with a cold engine and climb a hill, then start a long, slow, gentle descent. Suppose for simplicity that I'm traveling the same speed all the time.

1st 5 min: 20 mpg
2nd 5min: 50 mpg
3rd 5min: 80 mpg

The average weighting each 5 minute segment would be 50mpg, but the overall mpg weights each segment by the quantity of gas used. If the speed and distance traveled over each time interval was the same, the overall mpg would be 3 / [1/20 + 1/50 + 1/80] = 36 mpg.

This would be obvious and intuitive if we used L / 100km, gallons per 100 miles, or a sensible linear measure of fuel consumption instead of mpg. Is there avy way to make a USDM Prius sold in the United States display fuel consumption as L / 100km on the MFD? Anything to help take really high fuel consumption seriously and to not take very low consumption or very high mpg too seriously.

By the way, if the intervals with lower mpg are traveled at higher speeds consuming even more fuel, the nonlinearity over time would be even more pronounced.

ken1784 · Jul 16, 2006

<div class='quotetop'>QUOTE(theorist @ Jul 16 2006, 03:30 PM) [snapback]287075[/snapback]</div>

1st 5 min: 20 mpg
2nd 5min: 50 mpg
3rd 5min: 80 mpg

The average weighting each 5 minute segment would be 50mpg, but the overall mpg weights each segment by the quantity of gas used. If the speed and distance traveled over each time interval was the same, the overall mpg would be 3 / [1/20 + 1/50 + 1/80] = 36 mpg.
[/b]
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You're absolutely correct.

My point was edeng has no chance to get 50 mpg or higher.

Ken@Japan

edeng · Jul 16, 2006

<div class='quotetop'>QUOTE(ken1784 @ Jul 16 2006, 02:37 AM) [snapback]287089[/snapback]</div>

You're absolutely correct.

My point was edeng has no chance to get 50 mpg or higher.

Ken@Japan
[/b]
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Granted my trips are short and higher proportions of starts and lower mpg's are a factor. I'll check the bar graphs to see what they look like.

Again I ask, what is "pulse and glide"? My search for it yielded nothing.
Also one reply suggested I see "mpg sticky". What's a "sticky".
Please bear with me as a new owner and unfamiliar with the new (to me) acronyms used in the posts.

theorist · Jul 16, 2006

<div class='quotetop'>QUOTE(edeng @ Jul 16 2006, 08:39 PM) [snapback]287314[/snapback]</div>

Again I ask, what is "pulse and glide"? My search for it yielded nothing.
Also one reply suggested I see "mpg sticky". What's a "sticky".
Please bear with me as a new owner and unfamiliar with the new (to me) acronyms used in the posts.
[/b]
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Here's a nice summary from an excellent site frequented by hypermilers.
http://www.cleanmpg.com/forums/showthread.php?t=1224

Pulse and Glide technique: What SOC gives best fuel economy?

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