Prius Hybrid Fuel Economy Expectations For Psuedo-Hypermilers

[catgic]

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[bestmapman]

<div class='quotetop'>QUOTE(catgic @ Jul 8 2007, 04:21 PM) [snapback]475154[/snapback]</div>

Hybrid Pseudo-Hypermilers are those Petrol-Buck Saving drivers like me out here in the Hybrid Hinterlands who are neither “fish nor fowl,” when it comes to driving a Prius or other hybrid vehicle. Our day-to-day hybrid-driving techniques fall somewhere between those used by Gas-To-Go/Brake-To-Stop drivers and the 100+ MPG FE Hybrid Hypermilers.

We keep our tires “over-inflated” and otherwise work at applying Hybrid Hypermiling driving techniques when the terrain, traffic conditions and our “Darling, please turn on the air-conditioner,” conditioned air loving trueloves permit us.

I saw a need for a quick, visual reference that shows MPG FE “Expectations” vs. “Real-World” MPH. I put my “seaman’s eye” to my personal, real-world MPG vs. MPH log data and driving experience; known Prius quirks and operating idiosyncrasies; web posted personal log data and anecdotal comments; various theoretical calculations and test data, and came up with a “best-guess” graphical plot of the weighted composite merging of all this disparate data.

The enclosed chart, entitled “Prius Fuel Economy Expectations For Psuedo-Hypermilers,” is my attempt at creating a visual “Real-World, Quick MPG vs. MPH Reference.” It attempts to graphically capture and display the “expected, nominal” CITY and HIGHWAY MPG a Pseudo-Hypermiling Prius driver might obtain when driving over various ranges of road travel speeds.

Your personal fuel economy versus travel speed experience may or may not agree with or track the “expected, nominal” CITY and HIGHWAY MPG vs. MPH on my plot, but that is O.K. It is O.K. because, like the difference between grains of sand on a sandy beach, each Prius Hybrid Psuedo-Hypermiling driver has a different shape, size and driving technique.


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This pretty much matches my experience for phase 4. The only thing that I would ad is a seperate lines for the different phases. This would help explain the first 5 minute low MPH figures.

[catgic]

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[bwilson4web]

<div class='quotetop'>QUOTE(catgic @ Jul 8 2007, 03:21 PM) [snapback]475154[/snapback]</div>

. . .

[/b]

This approach starts with the drag formula for the NHW11 Prius reported by Toyota in Japan (thanks Ken) modified by a fixed overhead for the lighter secondary curve. To these curves, are data points from various benchmarks including the mileage log from the 2005 Prius marathon. It is always good to combine theory and data.

My earlier experimental data suggests that warm-up and temperature management have a major impact on on Prius performance. Other data points have been useful in quantifying the effects of oil level:


It is always nice to take theory and augment it by practice and taking care to site the sources.

Bob Wilson

[ystasino]

I just came back from a 6 and 1/2 hr 320 mile trip to the beach today, P&G between 55-65 mph for 60 mpg. Obviously this was not only highway as it included about 15 traffic lights and a lot of traffic on the bay bridge. It was not that slow, I have no mods, 44/44 psi and only 3000 miles on the new 07 Prius. I'm on my way to a 600+ tank with 585 mi already on the odometer and the guess gauge just turned to one solid pip. Overall mpg is 60.1. I hope this helps.

With the same traffic, traffic lights and +10mph I might have saved 20 mins and spent more than double the gas.

[catgic]

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[bwilson4web]

<div class='quotetop'>QUOTE(catgic @ Jul 9 2007, 02:51 PM) [snapback]475694[/snapback]</div>

. . . but mostly used Electronic Cruise Control (ECC) set at 66 MPH with manual foot throttle added to override the ECC in anticipation of upcoming hills-inclines. I also periodically interspersed use of “Pulse and Glide” where road terrain, travel and traffic conditions were accommodating. . . .

In general, if the Interstate road terrain, travel and traffic conditions are accommodating, and I am ambitious, I intersperse “Pulse and Glide” around my standard 66 MPH Target Speed (66 plus 4/66 minus 7) into the 99.9% of my driving that is done using a strict ECC controlled 66 MPH, as mentioned. . . .
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Have you done any compare and contrast studies of steady-speed, cruise control versus "Pulse and Glide" at highway speeds?

I remain skeptical about "Pulse and Glide" at speeds above 42 although I do advocate driving under strict ICE rpm (aka, power) limits. I advocate keeping the ICE rpm below 2,600 rpm and never exceeding 3,200 rpm. This is not pulse and glide but ICE rpm or power limit driving. Given the effects of terrain, it also looks like terrain driving. However, I have done some P&G studies below 42 mph and the results are mixed.

At speeds below 42 mph, I've used 25-43(34)P&G (25 mph minimum, 43 mph maximum, 34 mph average) and seen an 11% improvement over steady state 34 mph. However, 15-23(18)P&G was substantially worse than holding a steady speed of 18 mph.

In order for P&G to be a improvement over the equivalent steady-speed, the variable velocity, kinetic energy and ICE start/stop losses have to be lower than the steady speed, battery energy and ICE start/stop losses. This can be expressed as a family of equations that should map the Vmin-Vmax(Vavg) versus Vavg efficiency. In the positive area, there would be a net energy savings and in the negative area, a net energy loss. But this analytical approach only works cleanly at speeds below 42 mph where a true ICE off mode exists. The need to keep the ICE turning when at speeds above 42 mph complicates a high-speed model.

Bob Wilson

[ystasino]

<div class='quotetop'>QUOTE(catgic @ Jul 9 2007, 03:51 PM) [snapback]475694[/snapback]</div>

ystasino --- Thanks for the personal MPG data point. I assume the 60.1 is running MPG for that tank of gas as displayed on the MFD. It looks like we are driving similarly set-up machines. I am running with no mods, 46F/44R in the tires and turned 6000 miles on my odometer in June. During Florida’s “Room Temperature” winter and well into the spring time, before outside daytime ambient temperatures rise into the 80s requiring nearly full-time air-conditioner use in my car, I have regularly gotten 60+ Overall MPG for Mixed City, "Around Town" driving measured by the tank refill method.

I am familiar with the travel route, terrain and traffic dynamics over your travel route to the MD beaches. I lived in Annapolis, and have made that same ~220 mile round trip beach run across the Bay Bridge and down U.S. 50 to Ocean City, and the beaches. I would deem that drive as “Mixed Highway,” as it is not dedicated Interstate highway travel, and has occasional city-towns and cross streets-roads. In addition, the route is largely devoid of heavy semi-truck and commercial traffic which makes it compatible to unobtrusively employing the “Pulse and Glide” hypermiling technique over a 55-65 MPG range.

Doing the math, your 6 and 1/2 hr, 320 mile (I assume - round) trip to the beach was accomplished at an overall average trip speed of 49.2 MPH. Assuming a comfort break or two, a few stops at traffic lights and that your were probably running the air-conditioner in July’s hot weather during the 320 mile trip, your 60 MPG/49.2 MPH trip averages are impressive.

Making the trip 20 minutes faster, with the attendant added fuel consumption, would only have increased your average trip speed to 51.9 MPH and dragged you below 60 MPG. Going 10+ MPH faster would have brought you to 59.2 MPH for the trip and saved you an hour.
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Thanks for the analysis. You are correct the type of traffic was not interstate. I need to get uses to typing all the details which I was kind of tired to yesterday.

So I'll try to be more exact. These data were recorded by my brain but I was fairly focused since this was my first trip.

Outbound travel:
Start of traffic: Zipcode 21234; MPG 60.0; Miles on tank 275
1st stop: 8 miles later in downtown Baltimore; MPG 60.4; Miles on tank 283; ~time of travel ~ 20 min
2nd stop: 137 miles later to Red Lion at Berlin MD; MPG 59.6; Miles on tank 420; time of travel ~ 170 min
Final stop: Red Lion Berlin MD to Assateague state park: 10 miles; MPG 59.8; miles on tank 430; time of travel ~20 min

Inbound travel:
Start of traffic Assateague state park: MPG 59.8; Miles on tank 430
1 stop: Downtown Baltimore (21201); MPG 60.0 Miles on tank 577, time of travel 220 minutes*
Final stop Zipcode 21234; MPG 60.1; Miles on tank 585; time of travel ~20 min

*Stop and go traffic around bay bridge. Actual mpg increase during that traffic time 59.7 to 60.2.

A/C was set at 79 degrees throughout. Gallons pumped at previous stop: 9.567

I hope this helps and wonder how it fits your data.

[JimboK]

<div class='quotetop'>QUOTE(bwilson4web @ Jul 9 2007, 04:39 PM) [snapback]475725[/snapback]</div>

Have you done any compare and contrast studies of steady-speed, cruise control versus "Pulse and Glide" at highway speeds?[/b]

Hi, Bob. I actually completed such a comparison about a week ago, and I have a draft writeup I'd like to send you and a couple of others for peer review before posting, if you don't mind.

FYI, I've encountered some additional hurdles to the low-speed testing we've discussed. To avoid hijacking the thread, I'll share the details elsewhere later.

[bwilson4web]

<div class='quotetop'>QUOTE(JimboK @ Jul 9 2007, 04:05 PM) [snapback]475740[/snapback]</div>

Hi, Bob. I actually completed such a comparison about a week ago, and I have a draft writeup I'd like to send you and a couple of others for peer review before posting, if you don't mind.

FYI, I've encountered some additional hurdles to the low-speed testing we've discussed. To avoid hijacking the thread, I'll share the details elsewhere later.
[/b]

Excellent! I look forward to it.

If we can get a good model of P&G vs. hybrid steady-speed, we'll be able to map out where it makes sense and when it doesn't. This can lead to better hybrid driving habits with less angst.

Bob Wilson