Prius Prime Plus in my hands

That sure beats standing on brake and flooring the accelerator.

Bob Wilson

 

Getting the car ready Friday morning, I plugged in an 80W, 12V-to-120VAC inverter to power a Macintosh with GPS mouse and USB ports to power the iPhone 5s. I started the car to run the front and rear defrosters and heard a periodic whooshing sound to my right: ~10 second period for about 3 seconds. It sound like it was coming from the nearby rail yard. With everything working, I drove off and the sound continued.

My first thought was the passenger side, outside mirror motor was acting up but adjusting the mirror had no effect. Door or window mechanism, still no luck. So I pulled into a parking lot, left the car in "P" and went to the passenger side ... nothing. Then opening the door, there was that whoosh again . . . it was a small fan on the 80W inverter and realized I had the perfect sound-effect for "Dark Helmet":

It sounds a little like someone with a bronchial condition being told to "take a deep breath." Regardless, a spare t-shirt arranged around the fan outlet reduced the whoosh so it was only noticeable at speeds under ~40-50 mph. At highway speeds, I had to listen carefully to hear it and it soon became 'background noise.'

My 'to do' list:

• Cruise control minimum speed value and does it 'kick out' if the car dips below it
• mph vs MPG in HV mode: 25 mph up to 75 mph in 10 mph increments on a standard day
• Augmented with GPS, roll-down tests to calculate the three coefficients
• Review the trip GPS files (there were significant data gaps)
• Design a front curb 'feeler' to avoid crushing when parking front-in
• Mount the "KISS MY AMPS" frames front and rear
• Order "C55MPG" vanity plate and water-proof plastic bag to hold the cardboard temp tag
• Run out of gas to measure the true tank capacity and identify any error lights and codes
• Buy life-time alignment at local Firestone dealer and see what it arrived with at Huntsville
• Schedule early oil and transmission oil change with sample bottles for analysis
• Fully inflate the tires
• Payoff car loan

Bob Wilson

ps. Three flight legs came in at a total of ~33 gallons/passenger for ~1,200 miles, or ~36 MPG per passenger. Leaving the house at 5 AM and arriving at Providence RI at 2 PM or ~133 mph. The taxi and flight cost $140.

My return drive in the Prius Prime: 55 MPG, ~57 mph (block speed), and ~$40 once I refuel. I have some 'out of gas' tests to run.

 

There are three coefficients normally found in the EPA 'Test Car Data'

1. Target Coef A - constant drag force independent of velocity ... if it moves, it is there
2. Target Coef B - drag force proportional to velocity
3. Target Coef C - drag force proportional to velocity squared

Now I wish I'd never seen it. The only thing missing is the 'smoker' kit to return the flavor for that 'rolling coal' jerk running around Huntsville. Only I would mix in a little 'skunk oil' (see hunting.) Hummm, now that might work on tailgaters, especially the ones that like to flash their headlights.

Bob Wilson

 

I share your concern especially because I've not found a ".gov" regulation that specifies how to do a roll-down test. So I'm thinking someone decided a second order, polynomial with three coefficients would do a better job of curve fitting the data. But I've also noticed some ... anomalies in the coefficients reported by the vendors for different models.

If you have three coefficients, one can tweak them to give similar curves but go divergent beyond the roll-down test speed range. Also, there needs to be a statistically valid sample set and dealing with divergent data points. My thinking is:

• Bi-directional roll down starting at maximum highway speed, 75 mph, down to 25-15 mph
  • average the data points for each test
  • calculate the coefficients
• Do 5 sets and toss out the slowest and fastest of the bi-directional runs.
• Average the remaining three sets.

This protocol will give me confidence that I have usable coefficients for Prime performance curves.

Bob Wilson

 

Found it!

Source: Annual Certification Test Data for Vehicles and Engines | Compliance and Fuel Economy Data for Vehicles and Engines | US EPA

	EPA.gov	Prius 17	Prime 17
1	Set Coef A (lbf)	18.843	8.965
2	Set Coef B (lbf/mph)	0.17373	0.12237
3	Set Coef C (lbf/mph**2)	0.015138	0.014282

Whoot! Whoot!


Bob Wilson

 

My understanding is "set coefficients" is from the roll-down and "target" is for the dyno testing after factoring in the inertial load of the car.

Bob Wilson