During this morning's commute, I switched from the Energy screen to the Consumption screen. I kept my eye on the current (i.e. 3 second delayed) consumption level, which is much easier than watching the Energy flow.

As soon as the consumption fell below 50 mpg, I accelerated hard, generally up an upgrade, then backed off and came downhill at 75-100 mpg. I checked the Energy screen while this was happening and the ICE was on, but the consumption figure was still high.

Result: I upped my overall average for this tank from 49.6 to 50.8. It's not huge, but I had 175 miles on the tank before I started.

Northern New Jersey is pretty hilly and I had lots of opportunity to do this. I'm wondering if the P&G is necessary for those who travel on relatively flat terrain in order to take max advantage of the better efficiency of the gas engine when it's running at max RPM.

Anyone else have experience with this?

 

Hi,

I've done bike rides out of Belle Plaine, just N. of Cape Mays.

Anyway, here in Long Beach, Cal. my approach on the flat is bring the PII (Prius II) up to speed, than back off maybe 2 mph (now under 65 mph) and set the cruise control. While that doesn't always get me to 99 mpg, I'm quite happy to see 50+.

Remember, as I tell bike riders new to the sport, "the world is not flat."

 

I may just misunderstand what you are saying, but I'm pretty sure that you want to do the opposite: keep the engine load low as you climb the hill (as opposed to flooring it) and allow the car to lose a bit of speed as you climb. (How much, if any, should be appropriate to the traffic conditions.) Then you gain back your speed on the way down the other side. This is what folks commonly refer to as Driving with the Load, or DWL.
I always hear folks saying that it's better to accelerate very fast because the engine operates more efficiently at high RPM. And while it is true that a gasoline engine does make power more efficiently at open throttle, that doesn't mean that hard acceleration is a good use of that power. It takes a whole lot of gas to accelerate at such a high rate and odds are you will come out ahead of the game by keeping a somewhat lighter touch on the throttle.
My understanding of P&G is that it works due to the inefficiencies inherent to an ICE. At best, ~30% of the gasoline's energy makes it to the crank while the rest flows right out the tail pipe or out through the radiator. There are also losses due to mechanical friction in the engine and the losses associated with pumping air through that engine. When you take it off line (in the case of the Prius this is usually referred to as a "glide") all of those losses go away until you re-start the engine to get back up to speed. So in a way you are really not wrong, but it's a bit more complicated.
In theory, the best practice would be to DWL (losing speed) up the front of the hill, and then glide down the back-side, letting gravity give back as much of your speed as possible before you resort to starting the ICE back up and burning fuel again.
You Prius guys are lucky. So many FE tools right at your fingertips!

 

This works great as long as I have enough momentum to get up the hill -- and no one lurking on my back bumper!

When I don't have enough momentum to climb a hill, the ICE kicks on and the MPGs plummet to 20 or so. Pressing hard on the accelerator may take the MPG down to 15, but only for a few seconds. A light touch only seems to stretch out the low MPG longer.

So much of the discussion about high-milage driving seems to turn on how to prevent the ICE from running. But on hilly terrain, I've found that almost impossible, except for long downhills.

So if the ICE is going to run anyway, why not run it at it's most efficient, and use the power to get quickly to a point where it's no longer needed?

Anyway, that's what I'm trying for now.

Thanks for all the commentary.

 

Sad to say but peak efficiency is not necessarily full throttle and I haven't seen a chart that represents all cases.

Since you live in a lab with a lot of hills, let me suggest you conduct a study:

1) Same hill - get the topographical map to measure height and length.
2) Use different, constant speeds from bottom to top by setting cruise control
3) At bottom on entry to hill, zero the MFD and record the distance and MPG at the top.
4) Calculate the fuel burn to go up the hill (distance / MPG).
5) Repeat test at different speeds.
6) Try to group by temperatures within 5-10 degrees and little to no wind
7) Repeat test with full-throttle accelleration up hill

This would be a valuable contribution to our knowledge.

Bob Wilson

 

This will be very inaccurate. The MFD MPG display on the Prius only does whole miles. You need to use the trip meter to get tenths. I do not know if the MPG on the MFD is for the whole miles it is displaying, or the actual miles in 10ths (or 100ths, etc) but rounded to a whole number.

I do agree with your concept however. The ONLY way to find the break even point is to figure out how much gas you burned at x MPG for y seconds covering z distance in various scenarios

 

Originally Posted by bwilson4web
Sad to say but peak efficiency is not necessarily full throttle and I haven't seen a chart that represents all cases.

Since you live in a lab with a lot of hills, let me suggest you conduct a study:

1) Same hill - get the topographical map to measure height and length.
2) Use different, constant speeds from bottom to top by setting cruise control
3) At bottom on entry to hill, zero the MFD and record the distance and MPG at the top.
4) Calculate the fuel burn to go up the hill (distance / MPG).
5) Repeat test at different speeds.
6) Try to group by temperatures within 5-10 degrees and little to no wind
7) Repeat test with full-throttle accelleration up hill

This would be a valuable contribution to our knowledge. Or the topographical map, step 1.

I've got one hill, unfortunately by a school, that I can use outside of school hours. I'll start my testing next week with a practice run this weekend on Holmes Ave:

~0.6 mi - horizontal (0.97 km)
~120 ft. - vertical (36.57 M.)

UTM 16 535244E 3842768N (NAD27)

I'll use the cruise control to hold the speed, reset the MFD at the bottom intersection and take the reading at the crest of the hill. With the altitude and vehicle mass, we can calculate the total energy change versus the fuel burn from the MFD. Since it is midway on my morning commute, the vehicle will be fully warmed up and the battery at a nominal starting state for each test. I'll measure the slope distance this evening on the way home using a trip meter.

Since it is a residential street, I will be able to cover:

MPH
25
30
35
40
45 ** on weekends only

Will this speed range meet our requirements?

To test faster speeds, I'll have to use Brindlee Mountain, south of town. There is a lower flat section and I'll use at least a 3 mile run up to normailze the battery charge. On that hill, I can handle:

MPH
40 (** with flashers **)
45
50
55
60
65
70

Just a reminder, mine is an NHW11, 03 Prius. It would be nice if we could find an NHW20 Prius owner to do simular hill-climbing tests with their vehicle.

Bob Wilson

 

I'm up for testing it on my '06.

I have about 900 miles on the car now and put about 100 miles on every day. Will there be any "break in" effect? Should I wait until I get some more miles on it?

I'll try to use the same parameters as Bob's. I've got a 10 minute run before the hill so I'll be warmed up and charged. The hill has two lanes so I can go at a range of speeds.

I found this map:

UTM 18 564844E 4555972N (NAD27)

http://www.topozone.com/map.asp?lat=...ad27&layer=DRG

The altitudes are clearly marked as 448 at the bottom and 586 at the top. Can I assume these are meters so the vertical distance is 138m?

It looks like the horizontal distance is .9 km.

Could someone who's experienced at reading topographical maps please confirm?

 

I gotta hand it to you guys. . .conducting an experiment, working on an algebra problem, and incedently, driving your Prius. Good for you! I have all I can handle just keeping myself from being hypnotized by the MFD, for heaven's sake.

So, let me give you my best guess: Going up a hill at x velocity which results in (so the MFD shows) let us say 20 mpg. I increase the velocity to x+y, and now my MFD shows 15 mpg. Hmm. That's 5 mpg less at x+y than at x. My assumption would be I've used more fuel going up the hill at x+y than at x.

Now, I'm not driving just up and down that hill, but lots of other hills - some higher, some with a steeper slope. And, of course I'm returning the same route. So, here's my approach.

I don't know what the round trip distance is, but I would set the cruise control at, speed x, and run the RT at the same speed. At the end of the trip, of course, note your avg mpg. Than reset the MFD, and the next day, pick some other speed, set your cruise control and run it again. Continue the process, even in rain (snow maybe?). When you finally have all your results noted, all you need do is find the kinda day it is (going to be), set your cruise control, kick back and watch the rest of the suckers beat their chests helplessly as you roll up those miles per gallon.

Now, I have my own lab results which came very quickly as my wife drives the Prius infrequently. She's a pedal-to-the metal kinda gal. Two days ago she took my Prius's 50.5 avg mpg down to 48.5 in less than 10 miles. All before she had the opportunity to set the cruise control.

 

Hi,
Good deal but the altitudes are in feet. The darker 'brown' lines are at 100 ft. intervals and the lighter, solid brown lines are at 20 ft. intervals. Sometimes the chart will also have a dashed, brown line for 10 ft. contours but those are often difficult to read.

You want to identify a good "start" and "stop" point so you can reset your MFD at one and 'read the result' at the other. I would use the access road to the east of Eagle Lake for the start and the road to the right at the crest, the one just to the right of that unnamed hill at 617 ft. This will confine your fuel burn to pretty much the slope and avoid the run-up and run-out flats. Regardless of which landmarks you use, as long as they are the same ones, you'll be in good shape. I would read those altitudes as:

~450 ft. -> ~595 ft.

You can get the gradient distance with one of your trip meters. However, you can also measure the horizontal distance using the 'folded paper' technique. Fold a piece of paper and long the fold, mark the start. Then 'roll' the paper edge along the route to the stop point and make a second mark. Then use the paper marks to measure the horizontal distance. With a little trig and the trip meter readings we can verify everything is 'on the mark.'

BTW, you can use the "Large" Map Size and "1:9,840" View Scale to show the whole slope on one image. Make a screen snapshot and you're good to go.

Now we'll also need your vehicle weight (I use the specification weight plus my 240 lbs and 6 lbs/gal for the gas.) This and the altitude change gives you the potential energy change. If the starting and ending velocities are the same, there won't be any change in kinetic energy.

I'd recommend at least three samples at each speed but prefer at least five. With five samples, you can easily eliminate the 'out liers' and see the mean and median:


BTW, in the above chart, I choose MPH speeds that convert nicely to kph values. The X axis is MPH but it is trivial to mark the kph values. But no one seemed to noticed . . . perhaps I need to show both MPH and KPH scale values.

Bob Wilson