Hi Krousdb:

___Thanks for adding the Prius II’s, Speed vs. FE dataset.

___With that, comes a lot of questions … Are you setting up your Prius II like most hypermilers w/ high tire pressures, low kinematic viscosity synthetics at half way between the hi/lo mark, windows tight above 30 mph, etc.? How about acceleration? Fast but smooth enough to get the ICE up and running from launch, slow crawl up to cruising speed via EV with a smooth transition into the ICE, or something in between? Are there any tips/tricks on using Max Fan w/out A/C in a Prius II for summer temp hypermiling? I remember reading how you love cruise but have never read that you have “Driven w/ Load”? I ask this because I remember reading how a Graham Scanner helped Rick Reese nail down a 70 + mpg tank in his Prius I using that technique. I have also read about attempting to keep a Prius II’s HSD from Regen as well as Propulsion when attempting a long coast to a stop. It sounds as if you use the energy flow screen as feedback to guide a very light touch of the accelerator when coasting to keep regen/propulsion at bay? Do you use a similar technique in your Prius or are your travels more conducive to other, less intrusive FE techniques?

___I have so little experience with the HSD/eCVT based automobiles and you just never know when this kind of knowledge could come in handy

___Good Luck and thanks in advance.

___Wayne R. Gerdes
___Waynegerdes@earthlink.net

 

Wayne,
Before I answer your questions, let me explain a few things that I have discovered about HSD. As it turns out, there is a magic speed. On my Prius II that speed is 42 MPH. Maximizing FE is all about reducing resistance. The culprits are aero drag, tire rolling resistance, CVT/MG friction and ICE friction. Of course, one can reduce aero drag by driving slower. But one can eliminate ICE friction completely as long as the speed is below 42. This is because the MG’s reach their maximum RPM at approx 42MPH, which forces the ICE to spin to prevent damage to the MG’s. So at speeds above 42, the ICE must spin. This results in added friction which must be compensated for to maintain speed.

Wayne Wrote:
Are you setting up your Prius II like most hypermilers w/ high tire pressures, low kinematic viscosity synthetics at half way between the hi/lo mark, windows tight above 30 mph, etc.?

Tire Pressure:
I have experimented with tire pressures ranging from 35 to 60 PSI. I have found that there is not a measurable difference in FE at higher speeds (42 MPH or above), but that one can increase FE at lower speeds by two to three percent with 60 PSI compared to 35 PSI. The increase seams to be linear between 35 and 60 so I have settled on 50 PSI. I expect that this would give me a two percent advantage at lower speeds (Below 42 MPH) over those who run the recommended 35 PSI. These figures are based on the OEM Goodyear Integrity Tires.

Tire Break-in:
I have also recorded a significant increase in lower speed FE between new OEM tires and worn out (2/32nd tread depth) OEM Tires. The worn out tires, even after correcting for the smaller circumference due to reduced tread depth (approx 0.6% overstatement in FE), can outperform new OEM tires by 3-5% at 60 PSI. This would suggest that the rolling resistance of tires decrease as they are broken in.

Oil:
I use 0W-20 Mobil 1 Synthetic oil filled to the halfway mark between the hi/lo mark. However, I don’t have any good data that would suggest a benefit over 5W-30 conventional oil. I change my oil and filter every 15,000 miles. My next change is coming up soon, but since the 0W-20 is no longer available, I will have to settle for the 5W-20 Mobil 1.

Wayne wrote:
Are there any tips/tricks on using Max Fan w/out A/C in a Prius II for summer temp hypermiling?

Climate Control:
At higher speeds, my windows are shut tight. I use the fan until the interior temp gets up to about 83F. Above that I use AC set to 83F. At lower speeds I have the drivers front window open 3” and the passenger side rear window open 3”. This creates a nice cross flow. If that is not enough to keep me comfortable I use the fan. I do not use AC at lower speeds. During the colder months I wear a heavy coat, a hat and gloves. I rarely use the heater unless the outside temps get into the teens and 20’s.

Wayne wrote:
How about acceleration? Fast but smooth enough to get the ICE up and running from launch, slow crawl up to cruising speed via EV with a smooth transition into the ICE, or something in between? I have also read about attempting to keep a Prius II’s HSD from Regen as well as Propulsion when attempting a long coast to a stop. It sounds as if you use the energy flow screen as feedback to guide a very light touch of the accelerator when coasting to keep regen/propulsion at bay? Do you use a similar technique in your Prius or are your travels more conducive to other, less intrusive FE techniques?

Driving Style:
I have two distinct driving styles, which I will call standard and hyper mode.

Standard Mode:
Mostly I use the standard mode because it doesn’t take much effort. On the highway, I just set cruise control to 55 MPH and go. In city driving, during acceleration or maintaining speed uphill, I use the deadband technique. This means no flow to or from the battery while accelerating. I glide (no flow at all, ICE is stopped) during mild downhill stretches. I apply the brakes (regen) on steeper downhill stretches to keep my speed below 42MPH. When coming to a stop I coast (foot off the accelerator) to stops. While braking and coasting a small amount of regen is provided to maintain the battery level. Standard mode yields the FE data that I provided earlier. I use this technique on my daily commute which is 50% highway at 55MPH and 50% city at 35 MPH. Depending on environmental variables, during the summer my FE ranges from 67 to 72 MPG.

Hyper Mode:
Occasionally I have an opportunity to use hyper mode. The key to hyper mode is the “pulse and glide” technique. The main goal behind “pulse and glide” is to minimize energy conversion. Energy conversion occurs when you convert fuel into kinetic energy, when you store kinetic energy as potential energy (charging the battery), and when you convert potential energy back into kinetic energy (discharging the battery). Each conversion results in losses. It is estimated that the ICE is only about 35% efficient, and that charging and discharging the battery is 80-90% efficient. In general, the energy losses manifest themselves as heat.

The “pulse and glide” technique seeks to minimize the amount of time that the ICE runs, and minimize power flowing to and from the battery. The “pulse” refers to deadband acceleration (no flow to or from the battery) up to 40 MPH. Next comes the “glide” (ICE is stopped, no flow at all) where the speed slowly decreases to 33 MPH. The cycle continues until a stop is required, at such time the brakes are applied and some regen helps to maintain the battery level. Brakes are also applied if a downhill stretch causes the speed to exceed 40MPH.

On level roads, the rate of acceleration will be about equal to the rate of deceleration. That would suggest that the ICE will run approx 50% of the time. So the FE would be twice as much as the FE indicated during acceleration. I have recorded FE in the low 90’s on level roads.

Contrary to popular belief, a route with gently rolling hills can increase FE. This is because the “pulse” happens when climbing the hill and the “glide” happens during the descent. The FE will be lower while climbing but the “glide” will last much longer. On some routes, during “pulse and glide” the ICE need only run about 25% of the time, yielding a FE four times as much as the FE indicated while climbing the hill. I have recorded FE over 100MPG (estimated at over 104 for over 100 miles) on a route with gently rolling hills.

In some situations, the pulse technique might require modification if there is not enough regen (stop lights, braking to maintain 40 MPH down hill) to maintain the battery level. Even though “pulse and glide” does not use the battery to propel the car, battery power is required to start the ICE at the beginning of each “pulse”. Likewise, battery power is required to power the electrical systems (estimated at 600W continuous). If you notice the battery level dropping to 4 bars, change the “pulse” technique from “deadband acceleration” to “charging acceleration”. This is a slightly slower rate of acceleration where the ICE also charges the battery. The FE during acceleration is about the same but the ICE runs longer, so FE will decrease until your battery level recovers to 5 bars. If your battery gets below 4 bars, it is nearly impossible to glide (deadband), as the ICE will want to charge the battery.

Wayne wrote:
I remember reading how you love cruise but have never read that you have “Driven w/ Load”? I ask this because I remember reading how a Graham Scanner helped Rick Reese nail down a 70 + mpg tank in his Prius I using that technique.

I don’t understand what is meant by “Driven w/Load”. Can you elaborate?

Wayne wrote:
___I have so little experience with the HSD/eCVT based automobiles and you just never know when this kind of knowledge could come in handy.

I hope this helps! Now, can someone give me a similar tutorial on IMA? I wonder if "pulse and glide" would work well for IMA and if gently rolling hills are preferable to level roads.

 

For the benefit of all Prius owners, Krousdb's previous post has some excellent tips on maximizing fuel economy in your cars.

Seems like it would make a great article to add to the "Learn" section.

Regards,

 

Sweet spots for HSD differ by terrain and conditions.

That's not a fact, but merely my impression, I simply wanted to summarize the posting in the first sentence.
Just like everyone else here I have been interested in speed vs mileage relationships for my 05 Prius II, but I've come to the conclusion that there is no single relationship that can describe optimal efficiency vs speed, for all conditions.
In addition, while theoretically it is correct that the faster you drive, the greater the drag and the lower your mileage, there are instances where I believe that is simply not true for HSD, where if under identical conditions you would drive slower, your mileage would go down. My guess is that it relates to the programming of HSD operations, in terms of cycling of HSD components, and loading of ICE via generator, etc..
The reason I believe that is the case is my experiences driving in TX hill country. Specifically, the trip from Fredericksburg to Enchanted Rock State Park, about 16 miles one way, over hilly terrain, with altitude change. Repeated trips back and forth revealed (round trips!) that under identical conditions, if I drove around 50 mph, mileage would be well below 50, closer to 45 in fact, but if I stayed above 60 and closer to 65 mph, mileage jumped to 65 to 70 mpg!
The only way I can explain that relates to the specific nature of the hilly terrain: short but steep hills, up and down, up and down. At slower speeds, the ICE labors on the uphill, and instantaneous mileage is almost down to 10. Coasting down the other side it is high, but not always 99, since the ICE needs to charge the batteries depleted on the climbs. At a higher speeds, since the hills are steep but very short, I can ease up the inclines by starting at high speed and 'coasting' uphill while rapidly deceleration, and then accelerating on the downhills, and maintaining an overall high level of instantaneous mileage.
(see also the very informative post above by krousdb)
On a level highway, things obviously are different, but there may still be some similar factors at work. Traffic makes a big difference in terms of coasting or drafting. While this may sound silly, I have the distinct impression that when driving fast on a highway in a fairly dense group of cars, HSD benefits from the drafting effect of the combined traffic around you, and my mileage is much better than when driving the same strech of highway at the same speed without any traffic. In addition to the drafting effect though, I suspect the HSD is more efficient (in my experience) when not driving constant, but when continuously varying speed.
The same strech of highway I often drive at more or less the same speed (around65-70), I have gotten mileage as low as 42, and as high as 65, at different times, and my impression is that fast flowing traffic with not very constant speed increases mileage, while absence of any traffic, constant speed, and lower temperatures decrease mileage. Headwind also makes a huge difference (in our coastal regions).
I have also nopticed what others posted (based on instantaneous mileage readout), that under certain conditions driving for 15 - 20 minutes at 65 I get worse mileage than driving 15-20 minutes under the same conditions, at 68. However, the optimal speed for best mileage differes on conditions, and when there is little or no traffic, then optimal speed is lower than 65.
To date, I have mostly driven with the help of the consumption screen with the 5-minute avg mileage display, trying to adjust my driving to conditions in order to maximize these 5-min bars.
I really like the idea of krousdb of using the energy flow screen to minimize energy flow to/from battery although I'm not quite sure yet if I can wrap my head around that in an intellectual way:
while I understand that energy flow to/from the battery could be considered wasteful because of the low conversion efficiency, such flow at the same time increases overall HSD efficiency to some extent, by optimizing the load on the ICE and thus raising the thermodynamic efficiency of the ICE.
My guess is that this is precisely what Toyota engineers mapped for the programming of HSD, when to use a given amount of energy flow to/from battery, in order to maximize thermodynamic ICE efficiency and thus help improve HSD efficiency, and that is also why I believe HSD has sweet spots that differ for varying conditions.

 

Hi Krousdb:

___That was the best HSD hypermileage tutorial I have ever had the opportunity to read to date and I want to personally thank you for it. I had only a foggy idea as to what was going on in the HSD at or around 42 mph and you cleared a lot of my and I am sure others misconceptions up. I can only hope Jason makes your post and his thread a sticky. Actually, he could use the help in his Prius II

___I hope the following helps you in regards to IMA, hypermileage, and my experiences with it.

Tire Pressure’s: I ran pressures of 60 # for the record setters in the RE92’s and I would drop back to 52 - 56 #’s (normal leak off) for every day commuting.

Tire Break-in: Same thing with Insight’s RE92’s although I never had the opportunity to see 4 brand new RE92’s on my own at the same time. According to others that have replaced them with like for like, it is an ~ 3,000 mile penalty before they open up for maximum FE once again although no one has ever scientifically measured the actual FE delta from new on up that I have read?

Oil: Mobil1 0W-20 was its staple as it is in the rest of my automobiles. I horded a few cases so I have ~ 5 years worth for the Accord

___The following may be of some interest to you?

Kinematic Viscosities (ASTM D-445) of the respective manufacturer’s synthetic oils:

Mobil1 SAE 0W-20
cSt @ 40 degrees C = 43.0
cSt @ 100 degrees C = 8.4

Pennzoil SAE 0W-20
cSt @ 40 degrees C = 46.5
cSt @ 100 degrees C = 8.7

Mobil1 SAE 5W-20
cSt @ 40 degrees C = 48.3
cSt @ 100 degrees C = 8.8

Amsoil SAE 5W-20
cSt @ 40 degrees C = 49.6
cSt @ 100 degrees C = 9.0

Climate Control: Buttoned up tight at speeds > 30 mph. Two windows open from a stop to ~ the same 30 mph. Max Fan w A/C disengaged. Spray bottle and ice cooler on the 90 + degree days. This is where the Prius has me at a loss. Can you run max fan flow from the vents w/out A/C? I thought I remember reading that you could not?

Driving style:

Std. Hypermileage Mode: Accelerations held to just below or just into 4 bars of assist and backing off to remove them (IMA’s std. engagement and tough to keep out of in second gear) appeared to allow the highest FE over a given distance during accelerations. There was no forced or hidden charge hit later on to bring your overall down. This is slow and steady up from 1st all the way through 5th. Once in 5th w/ lean-burn, you would “drive with load” to maintain it. That is slowly decelerating on any uphill climb to maintain lean burn and slowly accelerating on the down slopes back to the target speed if there was no delta between initial and final elevations. This works very well with the non-hybrid’s too. Speeds ranged from 50 - 67 mph depending on the down slopes length and grade. Maintaining a relatively steady band between 45 - 54 mph on the flats would leave you highway legal but just barely. This was good for a usual 95 - 117 mpg depending on wind conditions in warmer late spring, summer, and early fall temps here in Northern Illinois.

Extreme Hypermileage Mode: Same accelerations and techniques but slower overall speeds. The record runs came about at 33 (DWL speed at crests) - 48 min/max speeds and driving at the absolute minimums out on rural highways. When driving locally, 33 - 35 mph at just above idle would give a relatively steady 125 - 135 mpg but local roads are not conducive for this over a longer period given the lights, signs, and traffic to kill off momentum.

___Pulse and Glide with an IMA is not quite the same as your description for the Prius II. The following works for max FE also but it depends on traffic conditions. The Insight with a quick 1 - 2 - and maybe even into 3rd w/out assist and forced autostop for a long coast afterwards would yield excellent results but traffic jams are never conducive to let the glide continue to a stop nor was it practical over a given distance. I experimented with 1- 2 - 3 - forced autostops and coast to an actual stop on a country road out near my workplace late last year. With that, I could maintain 140 mpg over 5 miles but it wasn’t practical to coast all the way to a stop after each pulse. In heavy traffic using maximum buffers, pulse and glide was all I had and with it, I could maintain > 100 mpg but because there is never a uniform gap opening up in any acceleration phase nor regular distance before you actually did have to grab some regen nor heaven forbid, use the mechanicals, I could only very rarely increase my p[resent FE in the heaviest of traffic. It was a lot of work to simply maintain the current FE so I disliked driving under those conditions as do most for the more normal obvious “I hate traffic jams” reason.

___The pulse and glide technique that you described with the Prius II would not help the IMA equipped Honda’s imho because the ICE doesn’t shut down. That is unless through a forced autostop. Very few IMA or non-hybrid drivers use Forced Autostops to maximize FE but in heavy and still moving traffic, it is most certainly available for those with a stick in particular.

Gently rolling hills were never conducive to maximums with an IMA equipped hybrid in my experience. The flats at the lowest RPM’s and in the highest gear were however.

___And something extra … Straight drafts were relatively useless in the Insight because she really didn’t have the power at maximum FE (maintaining Lean Burn in fifth) to keep up with the continuous ebb and flow of the target when attempting to maintain a proper close in. When you did find an 18-wheeler at a steady 45 - 48 mph on just the right section of roadway for whatever reason, you could peg the instantaneous at 150 mpg for however long the steady pace was maintained. Only on relatively flat terrain however. Traffic side drafts were the Insight’s godsend. Because of the slower speeds in the far right lanes vs. those in the middle and left lanes, the delta would help push her into a healthy average even when there was a headwind up to a max of maybe 10 mph. Out in the open with a headwind, maximum FE was very painful to achieve. As wind speeds climbed, this would become maddening until you were at a point when you needed 3rd gear just to maintain highway speed. I do not know if you have ever driven in a 30 + mph headwind in the Prius II yet but from my experience in the Insight, you do not want to do this … ever

___Good Luck

___Wayne R. Gerdes
___Waynegerdes@earthlink.net

 

Thanks everyone for the kind feedback and thanks to Wayne for the IMA turorial. I understand conceptually, but because I have never driven a Honda Hybrid, I am foggy on a few things. But maybe you can show me in person the next time I visit my parents in Aurora, IL. How far are you from there?

With regard to the fan, i have never tried the highest setting but I have run it one notch lower than high without requiring the AC. When you first turn on the fan, AC comes on automatically. All you have to do is turn off the AC and the fan will continue to run. Great idea about the spray bottle and ice. I will try that some time.

 

Hi MGBGT:

___The wind tunnel effect as you mentioned is a traffic side draft.

___For that continual climb/descent route you described, about all I can add is I hope you would attempt a DWL technique through that area. Steady speeds are FE killers in the hills in my experience.

___Finally, to give everyone a heads up as to Krousdb’s accomplishments, he has taken his Prius II for a max tank range of 967 miles at almost 86 mpg. This is in a NA spec’ed Prius II with the smaller bladdered tank, not the non-PZEV Japanese version with the much larger cap. I hope most are cognizant of what it takes to achieve this level of FE in a Prius II as well as how important his comments are for those interested in taking their Prius’ or any HSD/eCVT based hybrid’s to their limits.

___Krousdb, Aurora, IL.? I drive by that city every day! If you are ever in the area, drop me a PM as I would love to meet up with another hybrid/FE enthusiast. Although I do not own an Insight anymore, the same basic techniques work in the Accord, Ranger, Corolla, and MDX. If you happen to be in or around the area on July 17, you will have to come with us to the Wi./Il. hybrid group meet to see the Milwaukee Brewer’s at Miller Park up north in Milwaukee. There are a more then a few hypermiler’s scheduled to appear again this year and Ericbecky puts on a pretty nice show for all that attend

___Good Luck

___Wayne R. Gerdes
___Waynegerdes@earthlink.net

 

Thanks for the invite but that is a bad weekend for me. Keep me in mind for the next one.