how does the Prius measure fuel consumption and calculate its gas mileage?
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M$3 Answers
Excerpt
“Fuel economy is measured under controlled conditions in a laboratory using a standardized test procedure specified by federal law. Manufacturers test their own vehicles—usually pre-production prototypes—and report the results to EPA. EPA reviews the results and confirms about 10-15 percent of them through their own tests at the National Vehicles and Fuel Emissions Laboratory.”
Cars, including Prius, are tested in this way.
How Vehicles are tested is insightful on this subject matter.
Run through the “slides” and the video.
Dynamometer is used. The car runs on a schedule (standardized driving routine) by professional driver. A hose connecting tailpipe will collect the engine exhaust, which will then be measured carbon content. Fuel consumption is then calculated. See EPA detailed test information for different “schedules” of different tests needed.
2010 Fuel Economy Guide is available now. We can check Prius data there. We can also search it from here based on models/makes.
Hope this helps.
websites mentioned in texts.
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M$You can calculate your GPM here: http://www.mpgillusion.com/2008/10/tools-for-calculating-gpm-from-mpg.html
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M$
Hi Mbrourman,
Thanks for the clarification. I previously misinterpreted your question.
I have written a "new answer" in comment section of my answer.
Hope this helps.
Let me try to clarify my question - because the answers that I'm getting aren't really getting to the heart of what I want to know. What I'm trying to understand is -
a) what mechanism is actually being used to measure the fuel consumed (e.g. a separate fuel flow meter, or fuel pump run time, or fuel injector open time, etc., and
b) what algorithm is the car's computer using to determine the average mpg that is displayed (e.g. average since last fill-up, "moving average" with more weighting on recent driving, etc. ). There are times when the displayed tank average differs from my own calculation ( based on # of miles traveled on X gallons of gas pumped into the tank).
So how is the Prius coming up with that average?
You can leave an optional "tip" with Mahalo's virtual currency, Mahalo Dollars. If you are asking a difficult question that might require some research, or if you'd like a wide variety of feedback, a higher tip often leads to more answers to your question.
M$
Hi asianboy,
I've been voted unhelpful by you.
Hope you can enlighten me..
What in your opinion is "unhelpful" in my answer ?
Thanks in advance. :-)
I have mistaken this question as EPA’s Prius fuel consumption.
Below is my “new answer” for Prius built-in fuel consumption monitor:
Found an insightful Prius user website.
The introduction page has links to various Prius website where Prius users discussed and gave insights on their use of Prius.
For Prius fuel consumption,
http://prius.ecrostech.com/original/PriusFrames.htm
visit the url above, then click on “understanding of the prius”, then “making sense of the display”, scroll until “the consumption display”.
In the website, it talks about current fuel consumption, average fuel consumption, historical fuel consumption.
Some highlights: (refer to website for details)
1. Current Fuel consumption
Quote:
“….computed over a very short period of time, just a couple of seconds, but not continuously. There is a small lag between a change in engine conditions and the response of the display...”
2. Average Fuel consumption
Quote:
“…computed over the driving you've done since you last touched the Reset button...”
“Prius owners on the Yahoo! discussion group toyota-prius seem to agree that the average MPG figure shown by the consumption display is optimistic by about 2 MPG.”
The author figures that the error as 4%.
3. Historical Fuel consumption
Quote:
“For each five minutes that the car is turned on, whether in motion or not, the display shifts one column to the left and a new bar appears for the most recent five minutes. The left-most column disappears and is lost.”
“It is often possible to identify features of your trip, such as periods of cruising and stop-and-go traffic and to see how they affect fuel consumption. The first column after a cold start will show the fuel used to warm up the engine and catalytic converter.”
“…is cleared when you turn the car off”.
4. How fuel consumption is computed
Quote:
“Discussion on the Yahoo! group toyota-prius reached the conclusion that the car monitors distance travelled and fuel used and does some simple arithmetic to obtain the displayed values. This is the correct way to obtain a fuel economy average. Distance travelled comes from the same source as the odometer and trip meters, that is sensors on the wheels. Fuel use is probably measured by the fuel injection system.”
5. Regeneration stars
Quote:
“small yellow stars or diamonds…. These represent energy recovered through regenerative braking and simulated engine braking during that period. Each diamond represents 50 watt hours, or 180 kJ in units that make sense to me. “
6. Reset buttons
The author suggests 3 policies for resetting average fuel consumption calculation:
lifetime fuel consumption: never touch reset;
tank-by-tank fuel consumption: reset every time you fill fuel;
trip fuel consumption: reset when you begin a trip.
Hope this helps.