Max MPG driving uphill

in non highway speeds.
if there is nobody on the road AND you can allow your drop your speed down to as low as 20 mph.

While climbing a hill allowing momentum to take you up the hill rather than your powerplant is the most energy efficient method.

This experiment mimicks the Physics of an amusement park roller coaster using a 3rd gen Prius...

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Roller coaster Prius experiment
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If you are alone on a two way country asphalt road with a 30 to 45 mph speed limit ... try this ....

Your prius is in drive mode,
about 200 feet before an uphill road incline, speed up to 10 mph over the PSL
( e.g. if you have a 3o mph psl then speed up to 40 mph)
As your Prius starts going uphill, take your foot off the accelerator
put your transmission into Neutral.
(a 3rd generation Prius' still has can control over brakes and steering while in Neutral
so you can stop at anytime of this experiment if you think it is unsafe)

If the Prius speed is still over 20 mph AND it reaches the top of the hill THEN put the Prius back in drive mode
remember this hill as doable.

If the Prius speed drops below 20 mph AND it has not reach the top of the hill THEN put the Prius back in drive mode and
press the accelerator using the ICE to put you over the top of the hill.
remember this hill not doable . :-(

hope this helps

Walter

 

There is a simple rule of thumb:

• climb on engine only with no battery draw

The 1.8L engine is efficient over nearly all of the operating line. So climb using just the engine and do not draw power from the traction battery. The power flow arrows show when the traction battery being drawn down.

When dealing with traffic, one simple and very effective strategy is to look for large, semi-trailer trucks as the pacing vehicle. Their power-to-weight ratio makes their climbing speed pretty much optimal for any Prius climbing tall hills. Just follow one up in the truck climbing lane and the problem is solved.

This works for the NHW11 (2001-03) and the ZVW30 (2010-current.) In the case of the NHW11, it keeps the engine out of the highest power ranges that use a rich mixture to cool the exhaust and protect the catalytic converter. The ZVW30 in contrast uses cooled EGR to mitigate the exhaust temperature rise and keeps the mixture optimum so it can go up a hill efficiently about 5 mph faster. But don't take mine or anyone else's word . . . DO THE EXPERIMENT!

About six years ago, I did a series of hill climb test using just the starting and ending tripmeter to measure how much fuel was burned going up a local, 8% grade, hill:

Use the cruise control to set different climb speeds and note the entry and ending distance and MPG to calculate the fuel burned to crest the hill. It turns out 55-60 mph works just fine for the older NHW11. But reaching 65 mph and higher, the traction battery is being drawn down and this is bad news because it leads to a recharge later that heats the battery. The ZVW30 is more modern but the power-flow arrow technique works with it too.

Hills come in many different grades and traffic. But the simple rule of thumb, avoid drawing traction battery, is best not only for efficiency but a cooler, less-stressed traction battery.

Bob Wilson

 

This doesn't make sense when your destination is at the top of a long uphill. My beach house is at sea level, and I often go to a town that's at 15ooft above sea level. As I get near the town, the climb gets softer and I go under 40kph so I can switch to EV and use as much of the battery charge as possible. I get a full charge on the way down for free.

 

Sense has nothing to do with doing the experiment. When you see your own experimental data, you'll be able to make a better model of how the Prius really works. But it is your Prius and your gas.

My Prius work like our experiments have show.

Bob Wilson

 

I don't need experiments to conclude that I should start using up the traction battery when near a mountain summit, with the goal of having it "empty" just as I've began the decent.

 

Bob, since I'll be climbing some hills next week, I want to make sure I understand this. Looking at your chart for the NHW11, it looks to me like it says:
At 55 mph, it uses .072 gallons and gets to the top in 100 seconds.
At 80 mph, it uses .072 gallons and gets to the top in 69 seconds.

Does the purple outline show where the traction battery was being used and the blue outline then shows the most efficient range? I read this chart as saying you can get to the top using the same amount of gas in just a little longer time (100 vs 70 seconds) without stressing the traction battery.

 

You've got it!

This 525 ft / 160 m hill pretty well depleted the traction battery when I reached the crest. In one test, I actually had 'the turtle' show up and a traction battery too low which forced the car to slow down. Someone can climb a hill fast and draw extra power from the traction battery but it is an illusion.

Upon reaching the top, the car has to replace that charge and the mileage takes a big hit for about a mile or so. Worse, charging the traction battery to replace the lost charge heats up the traction battery. Doing a similar test three times on a hot Alabama summer led to the traction battery fan coming on. That is why I experiment . . . to know how the car really works with metrics and numbers.

Bob Wilson

 

How does the milage take a big hit when you are going down a steep mountain?

Regen is on, ICE is off.

Just a few days ago I run across this borderline scenario: completely depleted the traction battery just as I reached the summit, at night with NAV and lights on. The ICE came on for a brief moment while I was coasting downhill and picking up speed, a few seconds later with strong regen the ICE went off. It did cross my mind to perhaps not completely deplete the traction battery before the summit next time, but we are talking about the ICE being on for maybe 5 secs, there is no way that would make any difference.

 

I don't think it does, but you're assuming he goes right back down again. I have 2 hills where we go up and then level off for several miles before going down part way. The next hill rises some more and also drops a bit followed by a 3rd rise that then remains level until we head back home. In this scenario I believe the ICE will run quite a bit to recharge the traction battery.

 

Yeah that's a different scenario. I try to empty the battery when I know it's about to get a full charge via a big descend. The ideal scenario is driving around a mountain village in EV, prior to leaving and starting the descend.

 

That's why I wanted to make sure I understood what Bob was saying. I don't intend to do any tests next Tuesday, but I do plan to watch the display and do what I can to at least see what's going on. Trouble with some of these posts is too many look at them as a one-size-fits-all when they are just snippets of how the vehicle behaves in different scenarios. It's then up to us to apply them to our driving.

 

Theoretically, the faster you drive up a hill the less energy you will use (this isn't factoring in air resistance).

But if you drive over a hill at 40mph, you will use less energy then you would traveling at 30mph climbing the hill. but if you drive down the other side of the hill at 40mph you will gain less potential energy then you would driving down the hill at 30mph. one of the hills I regulary drive I normally hit the hill at 40mph then coast to the top so I drop down to 30mph at the top. this method only really gives you an advantage at lower speeds where air resistance isn't a big factor, if you was traveling at 65mph you'd probably loose more to air resistance if you tried hitting the hill at 75mph and dropping to 65mph on the the climb.


It seems to work for me at low speeds

I think this works because say you was climbing a hill that was completely vertical, you're having to overcome earths gravity of 9.8m/s (22mph per second), the longer you spend climbing that hill the higher the total potential acceleration you're having to overcome. if you took 10 seconds you'd have to overcome 98m/s (220mph) of potential acceleration over that 10 seconds but if you took 20 seconds to climb that same distance, you'd have to overcome 196m/s (440mph) of potential acceleration. You can apply this to the real world but it will only work upto a certain speed range

 

Any possibility of sharing the hill height change and run? Perhaps GPS coordinates we might use with Google Earth?

Thanks,
Bob Wilson

 

You appear to be confusing speed with energy. They are not directly equivalent.

The energy required to climb a hill should be proportional to the elevation change, but independent of the time used to perform the climb.

 

Wayne Gerdes at CleanMPG advocates taking long hills SLOWER. If you can do do without risking life-and-limb. If there a truck lane: use it, pretend you're a truck, hey that's all she's got.

 

True in theory, as long as your theory doesn't account for air resistance. Higher speed increases energy required per unit distance going uphill, exactly the same as it does going downhill or on level.

 

And Mikes1992's theory (post #33) is explicitly excluding that air resistance.

 

As long as you don't draw traction battery energy, you're at the right speed.

Bob Wilson