The city hill is not very practical. The light at the bottom is too easily red. This stops the steady state run-up. However, Brindle Mountain works:

65 mph -> 19.9 mpg (test run)
55 mph -> 20.6 mpg (test run)
50 mpg -> 21.8 mpg (test run)

distance: 1.5 miles
altitude change: ~530 ft.
temp: 81F

NHW11, 03 Prius, 240 lb driver, ~9-10 gal. fuel, 40 lbs. receiver hitch.

BTW, testing suggests a protocol that might be able to test how far back the MFD mileage covers. I have long suspected that there is a cut-off, either some "x" minutes or "y" miles that 'age-out' of the MPG display. If correct, it should be possible to use the run-up MPG vs. hill-climb MPG to determine how far back it goes.

Bob Wilson

 

Hi,

It might be helpful to know if that altitude of 530 ft for Brindley Mtn is from sea level (which is my guess) or elevation from its base. Maybe, maybe not Although, I guess assuming that your starting point for the climb is the base, (it looks to be a 6% grade). In other words, was your climb from sea level to 530 ft, or some other value? And is that info important? Or did I miss something?

centrider

 

My runs starts about 725 ft above sea level and ends about 1255 (see topographical map.) IMHO, I usually don't worry about desnity altitude effects this low until temperatures reach 85F.

Bob Wilson

 

Made my first run today on the hill:

.4 miles at 40 mph resulted in 17.2 mpg

Temp was 66 degrees, no wind.

I'm going up at a 6.5% grade (Bob's seems to be 6.7%).

I'll try a faster speed tomorrow.

One factor that might affect overall fuel economy is that, the faster I'm going at the top, the further I can coast down the other side. But I have no idea how to going about figuring the "sweet" spot. Any ideas?

 

We won't really know until the experiment is over. Sad to say, it will be two more months before we see temperatures like 66F in N. Alabama. However, 17.2 mpg @40 mph seems pretty low. That was with 'RESET' at the bottom and then reading the MPG at the crest when the instantanious MPG peaks out?

My worst, in the earlier model NHW11, was 19.9 MPG, at 81F (middle of the night.)

A quick sanity check:

1) oil level? (midway between E and F)
2) tire pressure? (42/40 psi)
3) vehicle miles? (68 k, 8k transaxle oil, 8k engine oil-Mobil 1 5W-30)
4) ICE air filter (8k)

Bob Wilson

 

I'm just coming up on 1K miles.

I've left the tire pressure at 35/33. But after the results of the tire pressure poll, I'm going to put it up to 42/40 tonight.

I'll repeat the 40 mph run tomorrow morning.

 

Here are some more hill climbing results:

I recently put new tires, Sumitoro HTR T4, 175/65R14 on my NHW11 03 Prius. So I checked the pressure and discovered that the Toyota service shop put just enough pressure to keep the 40 psi caps, green, 37 psi! Guess I'll have to get some 50 psi caps now. Regardless, I'm now running 50/48 psi on tires rated for 51 psi.

So the first thing I did was run Brindley Mountain hill climb tests:

Temp: 66-68F (recent cold front arrived)
Road distance: 1.5 mi. / 2.41 km.
Altitude change: 525 ft. / 160 M.
http://hiwaay.net/~bzwilson/prius/pri_power_Brindley.jpg
Weight: 2,765 lbs + 240 lb driver ~3,000 lbs / 1360.8 kg
Potential energy: 2,133,734 J.
Gallon of gasoline: 121 MJ.
MPG measured by RESET of MFD at bottom of hill.

Using cruise control, I got the following results:
MPH MPG Gallon Joules Efficency HP(hill-climb-demand)
35 22.4 .0670 8,107,000 26.3% 18.6
45 22.5 .0667 8,070,700 26.4% 23.9
55 20.8 .0721 8,724,100 24.5% 29.2
65 18.7 .0802 9,704,200 22.0% 34.5
70 18.8 .0798 9,655,800 22.1% 37.2
75 20.0 .0750 9,075,000 23.5% 39.8
75 19.5 .0769 9,304,900 22.9% 39.8

80 20.9 .0718 8,687,800 24.5% 42.4 (temp 84F, done later)
80 20.9 .0718 8,687,800 24.5% 42.4

I couldn't explain what happened at 75 mph. Curious, I repeated the hill climb later at 80 mph and gained a clue. The battery was contributing to the climb. At the top when turning around, the engine didn't auto-stop but kept running to charge the battery. Still, it was fun to climb the hill, passing all traffic at 80 mph.

Upon reflection, the hill climb test needs a 'run out' on the top to handle bringing the battery back to a normal state of charge. Otherwise, the short term battery contribution skews the results.

Battery Addendum:
NHW11 nominal energy: 961,200 J. (60%->45%, 267 Wh)
NHW20 nominal energy: 709,200 J. (60%->45%, 197 Wh)

NHW11 surge: 28 hp
NHW20 surge: 33 hp

Bob Wilson

 

So, Bob, what would be your recommendation as to the speed to negotiate this hill under consideration? ... Taking into consideration the efficiency of the vehicle, the amount of fuel consumed and the time spent in driving (faster climb & less time spent versus slower climb versus more time spent) ...?

 

I would follow the slowest truck or vehicle up the hill. But if there was none around, I'd probably set my cruise control for 55 mph.

Although it looks like 75 mph is as efficient, it is really just drawing down the battery. Once on the flat, the vehicle would get poor MPG until it has recharged the battery. That is why I need to repeat this series of tests with a run-out to the nearest town, Midway, about four miles down the road. However, I don't need to repeat the full series.

I'll do a 55 mph, 65 mph and 75 mph set and measure my traction battery charge level, start to finish. This will give a clearer picture of the energy state change.

One caveat, I would not do 65 mph going up the hill in my NHW11. That appears to be a 'bad speed' (tm). However, 60-65 mph is a great speed for flat land.

Bob Wilson

 

Here's my result on my local hill. I can't do the detailed calculations Bob did.


MPH MPG Temp

40 18.8 57
45 17.6 57
50 19.1 59
50 18.5 45
55 16.9 50
60 15.4 55

I repeated the 50 mph run, because the mpg was better than at the slower speeds.

This seems to indicate a "sweet" spot at 50 mph. I wasn't watching the power flow diagram. Could this mean that the electric motor assist kicks in at ~50 mph?

Does anyone have details about this?

The other thing I've noticed is a deterioration in my pump-calculated mpg over the 4 tanks. The first two tanks were 55 and 54 mpg. The last two have been 51 and 50 mpg. The only difference is that, for the first two tanks, I didn't reset the computer until I refilled. I'm wondering if seeing the running mpg for the tank helped me drive differently. Another experiment.