2001-03 Prius 65-70 miles per hour

Hi folks,

I recorded a trip from Huntsville AL to Knoxville TN using the ICE air flow for fuel consumption and MG2 rpm to calculate speed. Two cruise control speeds were used, 65 miles per hour and 70 miles per hour and the data generated this chart:



Several things stand out:

• cruise control variance +/- 2 miles per hour
• @65 miles per hour, ICE idle (backside of hills) gives +200 MPG
• @70 miles per hour, ICE idle disappears except below 70 miles per hour

Early on I found highway milage dropped off around 70 miles per hour and at 75 miles per hour, it was pretty low, 39 MPG. But this data shows the actual boundary is fairly sharp and suggests the mechanism.

The 2001-03 Prius, model NHW11, has a speed limit on MG1 rpm, 6,500 rpm. With an ICE idle speed of 1,200 rpm, that comes out right at 70 miles per hour. Sure enough, below 70 miles per hour, the ICE can idle with very low fuel flow. At 70 and above, the ICE has to run and burn fuel:
http://eahart.com/prius/psd/

The best strategy is to set the cruise control to the highest speed that still allows ICE idle and stays under 70 miles per hour. The optimum cross country, cruise control speed looks to be 68 miles per hour, 110 kph, as anything faster and MPG will take a hit.

There are a scattering of points up at 500 MPG but they are relatively sparse. I'll continue to look at the data to see if I can figure out what is going on. In the meanwhile, 68 miles per hour is my new, favorite cross country speed.

Bob Wilson

 

Hi folks,

I recorded a trip from Huntsville AL to Knoxville TN using the ICE air flow for fuel consumption and MG2 rpm to calculate speed. Two cruise control speeds were used, 65 miles per hour and 70 miles per hour and the data generated this chart:



Several things stand out:

• cruise control variance +/- 2 miles per hour
• @65 miles per hour, ICE idle (backside of hills) gives +200 MPG
• @70 miles per hour, ICE idle disappears except below 70 miles per hour

Early on I found highway milage dropped off around 70 miles per hour and at 75 miles per hour, it was pretty low, 39 MPG. But this data shows the actual boundary is fairly sharp and suggests the mechanism.

The 2001-03 Prius, model NHW11, has a speed limit on MG1 rpm, 6,500 rpm. With an ICE idle speed of 1,200 rpm, that comes out right at 70 miles per hour. Sure enough, below 70 miles per hour, the ICE can idle with very low fuel flow. At 70 and above, the ICE has to run and burn fuel:
http://eahart.com/prius/psd/

The best strategy is to set the cruise control to the highest speed that still allows ICE idle and stays under 70 miles per hour. The optimum cross country, cruise control speed looks to be 68 miles per hour, 110 kph, as anything faster and MPG will take a hit.

There are a scattering of points up at 500 MPG but they are relatively sparse. I'll continue to look at the data to see if I can figure out what is going on. In the meanwhile, 68 miles per hour is my new, favorite cross country speed.

Bob Wilson

 

<div class='quotetop'>QUOTE(Joekingiam @ Sep 19 2007, 07:45 AM) [snapback]514743[/snapback]</div>

I'm looking at pp. DI-81 of the 03 Prius Diagnostics manual, volume 1, and it shows both O(2) sensor voltages. The first one swings .25-.75 V and the second O(2) sensor swings about .6-.7 V. This is under code P0420. BTW, this is after running the vehicle for at least 5 minutes at 89 kph / 55 mph on top of an "idling warm-up."

Bob Wilson

 

<div class='quotetop'>QUOTE(douglas001001 @ Sep 19 2007, 12:56 PM) [snapback]514857[/snapback]</div>

Let me describe what I have recorded (it is a huge file) and we can talk:

GPS - recorded all NEMA text to a file
Graham Scanner - recorded these fields:
1) MG1 rpm (also provides torque at same interval)
2) MG2 rpm (also provides torque at same interval)
3) throttle airflow sensor grams/sec
4) MG2 torque (also provides rpm at same interval)
5) MG1 torque (also provides rpm at same interval)
6) battery amps

Using the 'end' times, I combine the following into rows in a massive spreadsheet:
1) GPS time-stamp
2) GPS latitude (degrees)
3) GPS longitude (degrees)
4) GPS altitude
5) scanner time stamp #1
6) MG2 rpm
7) MG2 torque
8) scanner time stamp #2
9) MG1 rpm
10) MG1 torque
11) scanner time stamp #3
12) battery current

To sync everything, I use the last records from the scanner and GPS recorder so the GPS data correlates with the Graham scanner data. The sampling interval is one second.

<div class='quotetop'>QUOTE(douglas001001 @ Sep 19 2007, 12:56 PM) [snapback]514857[/snapback]</div>

I tend to drive on cruise control as much as possible because it leads to reproducible results. However, there were segments at lower speeds. Certainly, I have no problem with sharing the data other than it is a bit large. The last time I checked, my spreadsheet was 27 MBytes.

Another alternative is using just the first hour, not all five hours. Would you be interested in a smaller sample? Any idea of the size limits for attached files?

Bob Wilson

ps. sample data headers:
Sat Cnt - count of GPS satellites seend
Sec - absolute seconds, UTC
trip sec - relative time to trip duration
Alt. - GPS reported altitude
Lo. deg - Longitude in degrees
La. Deg - Latitude in degrees
MG2 rpm -
MG2 Nm
Sec - time stamp for air flow data
Air g/s - throttle air grams per second
Sec - time stamp for following data
MG1 rpm
MG1 Nm
Sec - time stamp for battery current
Batt A - traction battery amps

Formula and Constants - handy constants and forumlas

Time - derived time stamp for following data
Alt - GPS altitude copied from column
M/sec - calculated speed based upon MG2 rpm and tire size
fuel g/sec - actual fuel flow
MG1 Nm - counter engine torque