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 miles per hour. 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 miles per hour, 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 miles per hour 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 miles per hour 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 miles per hour. 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 miles per hour 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.

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