Were these endurance test or ordinary use? If endurance tests, what sort of speeds?

Do the Japanese Prius have a bladder tank? I understand the European ones do not. If not, how many liters?

Thanks,
Bob Wilson

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Hi Bob,

They are both daily commuting plus some extra drive for the challenge.
The Teddy_Girl's result is the most impressive and details are...
http://www.cleanmpg.com/forums/showthread.php?t=1793
The speed is always below 42 miles per hour, of course.
They never drove on highway during the challenge period.
The Japanese Prius does not have a bladder tank.
Usually, we can put 49.5 liters on normal top-off, but we can put about 60 liters if the surface is incline and we have time more than 5 minutes.

Ken@Japan

I'm posting my reply here since it has Prius specific information:

My basic interest is understanding the degree that 'pulse-and-glide' makes sense in ordinary use. Although it may sound like heresy, I am beginning to suspect last year's 110 MPG Prius endurance record can be beat. But I'm not going to do anything until we have a good model that predicts performance.

Billy6 goes on the describe the recent Insight endurance test:
In a series hybrid like the Hondas, this makes sense:

1) accellerate to optimum MPG speed, 42 miles per hour using 'best practices'
2) glide to a stop or near-stop with ICE off
3) go to #1 while gas remains in tank

The resulting average speed should be no more than ~21 miles per hour. Sure enough, the average speeds were just under 21 miles per hour.

In the case of the Prius, ICE operation is not directly controlled like it is in the Honda hybrids. We operate various inputs to computers whose control laws operate the systems. However, I think we can 'reverse engineer' these control laws and come up with a usable endurance model. Once validated, it should be simple to test the 'limits' and determine the ultimate mpg capability assuming a perfect driver.

A model also lets us evaluate the 'street safety' of various pulse-and-glide parameters. What this means is we can use the 'lessons learned' from the Japanese and other endurance tests and determine where 'pulse-and-glide' makes sense and when it doesn't.

Now this is specific to parallel hybrid drive systems but in the case of Prius, any steady-state, flat road traveled at speeds below 42 miles per hour will automaticly function like a 'pulse-and-glide' system at a near steady speed.

Below 42 miles per hour, the Prius will shutoff the ICE and use battery power to maintain speed until the SOC gets low enough. Then the ICE will start, maintain speed on ICE while recharging the battery at a fairly efficient ICE operating point. Once the battery reaches a high enough SOC and triggered by a slight decrease in load, the vehicle switches back to battery power, a powered glide.

If that speed is 30 miles per hour (not counting warm-up and starting effects), the expected MPG in an NHW11 should be at least 95-99 MPG. Hills and overpasses cause other problems so this requires a flat road. I regularly use this technique in my evening commute.

To translate this into practice:

1) use flat access roads - they are often tolerant of vehicles traveling 30 miles per hour
2) accellerate to 31 miles per hour and set cruise control - this gets you to the right range. Let everything settle out including battery level.

3) 'pulse down 1 miles per hour' - to trigger battery assisted glide.
4) when the ICE comes on, 'pulse up 1 miles per hour' - this gets the car to a state ready for #3

Spend most of your time watching traffic and driving safely!

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.

When you say "accelerate" what is the rate? WOT? --- Richard

Hi Richard,
My data suggests ICE rpm works best below 3,500 rpm. Above 3,500 it looks like the specific fuel consumption (kW per unit of fuel) starts increasing.

If you are interested in looking at the data:

http://hiwaay.net/~bzwilson/prius/pri_power.html

There are links to excel spreadsheets with a lot of high quality data.

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.