Optimum Warp Stealth Technique?

I think it doesn't matter all that much. Like you, I've been experimenting with different approaches to maximize mileage, but at the end of the day, I'm going to keep this car for a long time and I'm going to get sick of "goosing" the accelerator and I'm just going to drive the thing.

When I drive in town, I very often accelerate in only the EV range from one stop sign to another. Other times (in town), I pulse up to 25 MPG, staying in the ECO range. Once I reach 25 MPH, I back off of the accelerator and then accelerate back into the EV range to maintain my speed. I don't get too obsessive-compulsive about this, and I don't think anyone should.

On the freeway, I've been trying a variety of things. I have an 85 mile r/t commute over very flat land. Sometimes there's a ton of traffic, other times it's light. But I ran the car about 200 miles over this commute at about 50 MPH, and the mileage hit 61.6 (as measured by the Prius gauge). My actual mileage was 57.6. After that, I filled up and commuted at 65 - 70 MPH. My mileage dropped to about 52 MPG actual.

I think my experiment was pretty extreme -- 50 MPH on a freeway is not entirely safe or practical. In the process of experimenting, I've been learning that the real key to good mileage is to use a light foot on the accelerator. Obsessing over whether the ICE starts up or not is not terribly safe or fun, and it makes very little difference in your mileage. If you generally drive without jackrabbit stops and starts, and you learn how to brake gradually, you develop habits that maximize mileage without going to the obsessive extremes that are used by... uh... the people who are about to flame me.

As for my mileage (shown below), it typically falls dramatically over the weekend, when I drive my family all over the place. A loaded car full of kids gets lower mileage, but when you think about it -- a car with two people gets twice the mileage, so with five of us in the car, my 50 MPH is effectively 250 MPG.

 

I agree with 'Rebound' and drive the car pretty much like I drive our 1.5L NHW11:

• warm-up - I try to use "N" as much as possible until the first auto-stop. In the ZVW30, it takes about 1/3d the distance as our NHW11.
• gentle in first 5 minutes - try to avoid speeds above 40-45 mph to let the transaxle and engine finish warming up.
• speed limits - actually I've always preferred just under the speed limit on cruise control so I can mull about other things. If there is a slow vehicle, I use it as my pace car, never tailgate, and enjoy the trip.
• choose route wisely - sometimes an access road provides the same distance at a slower and less 'intense' driving experience. Taking a 'short cut' at slower speeds doesn't hurt the elapsed time and saves beaucoup fuel and stress.

I'm not obsessive-compulsive enough to drive that way ... I like to enjoy more than just the vehicle.

Bob Wilson

 

:flame:

 

Welcome to the geeky world of excessive acronyms as a way of showing the size of your (ahem) "intellect"...

I think another way of stating your quetion (a question I share) is, "Is there a sweet spot for electrical propulsion (EV) when gliding? And if so, where exactly is it on the Hybrid System Indicator (HSI)?"

The theoretical "sweet spot" is, of course, to use zero EV. Any time you're drawing power from the battery, it has to be recharged, and there are losses. But if you're accelerating primarily from the gas engine (ICE), and making a lot of stops, you'll have surplus electricity, so you might as well use it - and since using it to accelerate with EV is often impractical, you may want to use it for gliding instead.

So where is the electric mode most efficient? 5%? 25%? 75%? The sources you reference suggest that since electric motors develop lots of torque at low RPM (revolutions per minute), it seems like the low-end of that range is likely to be the better choice. And considering that EV mode doesn't generate much additional "oomph" in the upper half of its range, I think they are also right in stating that higher output just means faster battery drain without much additional propulsion.

Of course, the system will automatically draw down the battery if the state of charge (SOC) is too far above the high limit - it will just send some juice to the secondary electric motor/generator (MG2) to push the wheels a bit and take a little load off the ICE. There will also be times when the ICE is generating surplus electricity, and some/all of that will be bled off in the same way - frequently, the hybrid system tries to "balance" the generated power vs the power used so that the battery is neither charged nor discharged. (unfortunately I think there are inverters - two of them - which still are part of the equation)

Bottom line: until somebody can post an official engineering doc showing the power/efficiency curve of the electric motors, I'm leaning toward the assumption that the bottom quarter (25% or less) is the best place for gliding. And I will vary how much (5%-25%) depending on upcoming stop lights and/or hills - less when the battery won't be recharged/overcharged, and more when I know regen or a hill climb will be providing surplus.


On the highway, it's easier to overshoot the sweet spot of the ICE when accelerating - the opposite of what happens at low speed (where it's easier to UNDER-shoot). You might see a slight gain in MPG (miles per gallon) by "pulsing" gradually and then gliding slightly, but I doubt it will be measurable unless you adapt it to the terrain - making use of downhills to accelerate without overshoot.

 

Remember that the HSI is NOT a tachometer... At low speeds, you can push it all the way to end of the PWR zone and still be in the sweet spot. At high speeds (75+), you may be outside the sweet spot while the HSI is still inside the "ECO" area.

 

You might try: CleanMPG, An authoritative source on fuel economy and hypermiling. Everyone needs a place to call home and that is a good place to learn their terminology and practices.

There are four known Prius models:

• NHW10 1997-2000 - sold only in Japan, it is the very first Prius. Some might call it Generation 0 or Sue, the model is NHW10 and came with the original 1.5L engine and individual cell, traction battery.
• NHW11 2001-03 - sold in Japan, North America, and a smattering around the world. Some call it Generation 1, it was the first sold in the USA.
• NHW20 2004-09 - sold in Japan and world wide, it was the last of the 1.5L Prius with a much improved traction battery and other advanced systems. Some call it Generation 2, it was the second model Prius sold in the USA.
• ZVW30 2010-current - sold everywhere, it is the first of the 1.8L Prius with significant power plant, transaxle, and power electronics improvements. It also includes European pedestrian safety features.

The USA has a funny concept of "model year" that allowed us to buy a 2010 Prius in late May 2009. Many other parts of the world would call it a 2009 Prius but then the Prius bought in January through mid-May would be . . . confused. I'm interested in precision and knowing exactly what model of Prius we are discussing so I try to always use the model identifier. I don't cotton to the "Gen <number>" since we typically don't count from zero unless we've spent too much time with computers. Model identifier eliminates any ambiguity since it is stamped on the vehicle frame.

Bob Wilson

 

As little of the little triangle filled in as possible, none is best. When you come out of warp stealth or regular highway driving, it will transition to regular engine totally off stealth at around 42 MPH, a left over artifact from the Gen II.

Wayne

 

Have been experimenting quite a bit with P/G and W/S with my new Prius and have noticed two apparent anomalies.
First, my commute has a 1000 foot mountain right in the middle of it. Coming down, I get to "gain back" some of the battery power I use going up, and I also gain my elevation premium back, minus system efficiency, of course. But what's really interesting is that there's about a four mile fairly level stretch that's actually very slightly downhill at the base of the mountain, leading up to a red light. When I try to hyper-mile this, I often get into a "zone" where I'm actually indicating about a quarter of the way into ICE, but my mileage indicator is "pegged" at 100 mpg, yet, I'm going 55-60 mph. I thought 41 mph was the max for such efficiency, due to the ICE having to be "on" above that speed?

The other anomaly I can't understand has to do with the warm-up period. There are times when I'm about 2-3 minutes into my commute when I P/G and "see" 100 mpg on the indicator, but I hear the engine running. Also, the cumulative mileage ticks down (this is most apparent when the tank's fairly full and, thus, the trip counter was just reset). So the mpg indicator seems to be reading some combination of pedal position and "coasting," but doesn't really calculate the engine still warming up.

Anyway, still learning to drive this little gem, but I must say I love it. On my third tank of gas, around 300 miles so far, and an indicated 60 MPG, which I think is good, given that mountain I have to go up and down every time I drive.

 

Based on what I've read others here say, what is happening is that the ICE is spinning, but not due to the force of combustion. Instead, I *think* that what happens is that power is applied to MG1 to reduce its RPM. Given that MG2's RPM is directly tied to tire rotation rate, and MG1's RPM is being capped by the computer, the result is that the ICE has no choice but to rotate, but it's really the tires/MG2 and MG1 that are causing it to rotate, not gasoline.

I could be wrong, but that's my impression anyway. Oh, and if you haven't seen it all ready, check out this nice page with an enlightening widget about the PSD.

 

On the first anomaly, if the road really does have a slight downhill, it is possible to be burning some fuel, but little enough that you really are getting over 100 mpg. To see the real MPG, put in a ScanGauge, which pegs far higher.

Also, if you just descended 1000 feet, your HV battery status is likely showing 8 bars, not the normal 6. The car wants to burn off these extra bars, and will use extra electric assist into the right half of the HSI bar to do this. This can result in either all-electric operation a ways into the normal ICE section, or enough electric boost to noticeably reduce gas use, producing abnormally high MPG. It won't last long.

On the second anomaly, during warmup, are the 100 mpg bar and the MPG downtick occurring simultaneously? I can explain them separately, but not together. That is, unless the later is a delayed response to a pulse that ended a few seconds earlier. That display has a slow update cycle.

 

Good explanation on the downhill run using extra battery juice - that is consonant with what I'm seeing - the battery goes down pretty fast after being pegged out with the downhill run.

On the second thing, I'll have to watch next fill-up - the odo has 300 plus miles now, and the economy changes too slowly to see it, but, yes, when the tank had just been filled and the trip reset, it was ticking down my MPG, even as it was showing 100 MPG - this a couple minutes after pulling out of my driveway, when engine wasn't fully warmed up. I'll verify as soon as I can and see if it happens again. It almost seems like the MPG bar is reading parameters for a warmed-up ICE, and doesn't know the engine is running, but I'll check it again. I might have not observed this correctly.

 

Terrain has a huge effect on mileage too. I've had mpg swing from 45 to almost 70 depending on the terrain (and traffic). For example, long inclines from a full stop are killers. So, my goal is to maximize mpg for a given route. On some routes, 45mpg is an outstanding result.

 

Based on other threads that I've seen, the choice between the first two options is more preference than anything. On a flat road, I haven't experienced significant difference. On hills, a manual approach provides a slight benefit over cruise control if you can adjust for terrain e.g., gradually give away a bit of speed on an uphill.). But most folks tire of micro-managing the car like this after a while. I drove from Atlanta to New Orleans recently and had great fun adjusting for terrain. After about an hour, though, I chose to enjoy the sunset instead.

regarding option (c) I havent found it to be helpfull at highway speeds. Even for a low resistance vehicle like a Prius, the wind resistance would bleed off speed to get any meanngful glide time on flat terrain.