Gliding above 55 mph & other observations

I drove up to & back from Roanoke, VA to visit my mother-in-law yesterday. All interstate driving (I-64 & I-81). About 380 miles round-trip with lots of rolling hills. I decided to use cruise control (set at 58 mph) to see how much of hit I would take on mpg versus a manual warp stealth technique. Two interesting observations.

1. On several occasions, my Prius put itself into a pure glide for 4-5 seconds, followed by regen, then back to pure glide for another 4-5 seconds, & so on. That's right, folks. Pure glide. No energy flow at all. How can this be possible? Had I seen no energy flow for just 2 seconds or so, I would have simply concluded that I was observing just a normal transition between regen & warp stealth or another mode. However, this was definitely not just a short transition. I realize the ICE must spin to prevent damage to MG1 (or is it MG2?) at speeds above 42 mph. Again, my cruise control was set to 58 mph. Therefore, did my eyes deceive me? What did I actually observe?

2. The cruise control did a much better job at maximizing fuel economy than I ever could with manual warp stealth (on hilly roads). While I'm certainly not a "master" when it comes to employing warp stealth, I do consider my technique pretty darn good. To my surprise, the cruise control was able to get the MFD to show 99+ mpg on several occasions where the grade was actually on a slight incline (uphill grade). I could never accomplish this manually, without a slight reduction in speed. This has me thinking that cruise control is actually better at these higher interstate speeds. On this particular 377 mile trip, I averaged 60.3 mpg using cruise control set at 58 mph. I always thought cruise control could not outperform the driver in terms of fuel economy. Did Toyota do something different to the program logic for cruise control in the 2007 Prius?

Please offer your comments/explanations.

 

<div class='quotetop'>QUOTE(ken1784 @ May 13 2007, 03:38 AM) [snapback]440962[/snapback]</div>

I understand now. Thanks, Ken. I just always thought that no energy flow on the MFD indicated that the ICE is completely off and not spinning at all. Guess I need to install something like Scangauge II, if I really want to see what the ICE is doing.



<div class='quotetop'>QUOTE(ken1784 @ May 13 2007, 03:38 AM) [snapback]440962[/snapback]</div>

Yes. It can be quite exhausting to manually employ/optimize warp stealth on long trips. I will definitely use cruise control from now on... at least on long trips. However, I am going to experiment with cruise control on shorter trips as well (less than 30 miles) and on various roads (level, hilly, etc...) to see if I experience similar increases in mpg with cruise. This will all be at interstate speeds, of course (between 55-65 mph). At speeds below 42 mph, I am certain cruise cannot come close to matching my FE with manually induced pulse & glide.

Thanks again for the feedback. I was starting to wonder if my MFD was just playing games to me with some of the results I was seeing.

Regards,
Pete

 

<div class='quotetop'>QUOTE(bestmapman @ May 13 2007, 04:39 AM) [snapback]440969[/snapback]</div>

Bestmapman. Nothing else special, really. My tires are set at 42/40 psi. It was warm yesterday (lower 80's I think) with very light winds. My 07 Prius has about 3700 miles on it. So, perhaps the engine is now broken-in and I'm seeing a slight boost in FE as a result. I can't take the credit for this trip. The cruise control did all the work! I just sat back and smiled whenever I saw the MFD showing an instantaneous reading of 90+ mpg.

<div class='quotetop'>QUOTE(JimboK @ May 13 2007, 09:50 AM) [snapback]441023[/snapback]</div>

Good morning, Jim!

Yes, that drive to Roanoke can definitely wear you out if you try to manually warp stealth & glide. As you know, there are some killer hills, especially the one on Afton mountain. If you ever find yourself driving up to Roanoke, please let me know what type of FE you get without CC. As mentioned in my reply to Ken, I probably need to invest in a Scangauge if I hope to do better than CC (at interstate speeds).

 

<div class='quotetop'>QUOTE(daniel @ May 13 2007, 10:03 AM) [snapback]441030[/snapback]</div>

Thanks, Daniel. The posted speed limit along this particular route is 65 mph, mostly. Must have been lucky yesterday, cause I didn't get any middle fingers or blown horns. :lol:

Come to think of it, no one has ever made any of these gestures to me... and I consistently drive beween 5-10 mph below the posted speed limits. I'm sure it's just a matter of time!

 

Thanks, Hobbit. Great explanation. I understand that the plateau/band at which you can enter Warp Stealth mode will vary with the battery's SoC. The higher the SoC, the wider the allowable operating range for WS. I find that when I'm driving on the highway or interstates (regardless of the prevailing grade), my SoC is always very high (at least 6 blue bars and even 7 or 8 green bars after a long downhill descent). Due to the terrain or traffic patterns, I am almost never able to stay in warp stealth long enough to bring my SoC down to 4 or 3 bars. If I remember reading correctly, it only takes a kilowatt or two of battery power to maintain WS. Therefore, I would think one would have to travel a great distance in WS mode to bring the battery's SoC from 6-7 bars down to 3-4 bars.

Therefore, in theory, it should be very easy for me to manually enter WS mode. And, I do find that to be the case when I'm on level or downhill grades. Where I believe cruise control may do a better job than the driver (at maximizing fuel economy) is on uphill grades. While climbing medium to severe hills, I can never get the MFD to report as high instantaneous mpg readings with manual pedal control, as I would observe with the cruise control on. This has me thinking that cruise control is better on climbs and manual control is better on descents and on level grades. I'd like to test this theory some more with more road trips to Roanoke (using the exact same route). In the mean time, what do you think?

Regards,
Pete

 

<div class='quotetop'>QUOTE(danatt @ May 14 2007, 09:50 PM) [snapback]442077[/snapback]</div>

Nope. Hardly any wind that day. Besides, I've never driven a complete route where the benefit of tail winds offset the losses from head or cross winds.