Prius Hybrid Fuel Economy Expectations For Psuedo-Hypermilers

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

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.

 

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

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

 

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.

 

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

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

 

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

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.

 

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

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.

 

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

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

 

<div class='quotetop'>QUOTE(catgic @ Jul 9 2007, 06:50 PM) [snapback]475815[/snapback]</div>

This is good. I was curious about your methodology and keeping records is pretty much what I've done over the years. Typically I used a student exam book and recorded my fill-ups. I'd track my MPG and if it fell off, I knew some maintenance was needed.

I'm interested quantitative numbers and modeling our Prius. This can lead to insights about future improvements. So not to worry, I understand and look forward to sharing.

Bob Wilson