"Help other Prius owners! Ever run your pack dry?"

Not exactly dry. NHW11 Prius will discontinue cruise control when battery SOC falls below about 45%. Feels like game over until you remember to press the accel pedal, then it climbs normally. Which is to say, somewhat noisy.

Climbing a sufficiently long 13% grade at 45 mph will accomplish this.

DAS

 

Indeed. I guess what I still don't understand is why this must be the path however - couldn't they just lock MG1, let MG2 spin freely, and run the ICE when torque demand matches ICE torque output? It seems like it'd be more efficient than anything including the Civic drivetrain... .

I live on the 101 but I don't know what part you're referring to as it's a very long highway. I live in Los Angeles, in the Valley. What section are you referring to? The section climbing up out of downtown?

Here's my experience with the Prius and hills:
The 101 coming up out of downtown is a moderate but long hill. Accelerating or maintaining speed on this hill is a non-issue for the Prius. You won't be racing anyone coming off the line at Highland but normal driving is fine. However, you do pay a serious MPG penalty - going up it I typically get 30-35mpg. Going down it I've gotten as high as 90mpg.

There are steeper hills however. The 70, which connects the 405 to the 5 going south to San Diego, is a mountain climb and descent. During the climb I could not get the Prius to maintain speed (and certainly not accelerate) - nearly flooring it caused me to decelerate from 72mph to 46mph. 46 is dangerous on a highway, especially a California one... .

All of that said, driving a Prius is not the same as driving a normal car because if you buy it, you want efficiency. My best MPG for climbing hills comes when I accelerate to a very aggressive speed on the flat or downhill, then take the hill and allow it to decelerate me. Of course, sometimes these wide variations in speed are impossible in traffic; the worst thing to happen in a Prius is to have someone stop hard in front of you on an uphill, because the next thing you're going to have to do is start from 0 doing what it does worst. If you're on a highway, you may as well turn your Hazards on when you start moving because you are not going to return to speed at the rate of traffic.

 

Hi,
I too had once thought about this until this week. Someone pointed out that "energy re-circulate" mode puts the engine in a high-torque, low-speed, very efficient power mode. "Energy re-circulate" is an infinitely variable 'overdrive.' But if MG1 were locked, the ICE-to-wheel ratio would be fixed and the ICE speed would have to vary in proportion to the speed. This would lead to operation in inefficient speed ranges.

One thing you might try is find one of the Prius transaxle models and see what ICE and MG2 speed ranges are available with MG1 set to zero. Treat 1,200 as the lowest ICE speed and 5,000 rpm as the maximum for your NHW20. Use 2,400 rpm as the threshold speed between efficient engine and higher gas consumption.

One thing I've been toying with is adjusting my throttle setting to put MG1 torque as close to zero as possible. I'm doing it just to find out if it is practical.

Bob Wilson

 

Well, what I'm asking is for cases where the speed and torque demands both match the ICE's output, why not let the ICE drive the wheels directly (or "lock the ICE-to-wheels ratio" as you engineeringly put it)? Although the majority of the "overdrive"/recirculate cases are obviously more efficient than a locked ICE ratio (because of very low torque demands), if a driver made a habit of accelerating along the ICE's power curve, these periods of acceleration would seem to benefit most from a locked MG1 and a free spinning MG2.

On recirculate mode itself, although I get how it works what I still don't understand is how the planetary gears actually interact in this mode - we've covered that the ICE is turning slowly and the most is being made of the low torque it's producing (some to the wheels, some to MG1). But what leads to the high RPM needed for this situation - is it MG2 + ICE? I'm basically asking how the gears "add." For example, does MG2's turning in this mode reduce or increase the stress on the ICE?

One thing that still confuses me about the Prius is that I've gotten as high as 60mpg and as low as 30mpg on the same stretch of low-traffic highway going the same speed (~85). I wonder if a scanner would tell me recirculate mode is in use in the 60mpg case and normal mode in the 30mpg case. Of course if I knew that for a fact I'd feel frustrated I couldn't slap the computer and tell it to switch over.

 

Welcome to the leading edge of Prius studies!
This is an area worthy of investigation. I have the characteristics for my NHW11 and can work out the model manually. But I haven't done much beyond some preliminary investigation using:

http://eahart.com/prius/psd/

Graham Davies did some the best work in this area:

http://prius.ecrostech.com/original/PriusFrames.htm

"MG1 = 3.6 * ICE - 2.6 * MG2"

MG1 - MG1 rpm
ICE - ICE rpm
MG2 - MG2 rpm

MG1_torque = 28% * ICE_torque (again from Graham Davies)

Notice that if you have any two of the rpm values, you can always calculate the other. Also the MG1_torque tells the ICE_torque.

WELCOME TO MY WORLD!

Bob Wilson

 

Thanks for the link Bob, I found the page within the frames that describes the adding more clearly. It's too bad those frames can't be more easily linked into. Great read though.

As for 30mpg vs 60mpg perhaps I'm better off staying uninformed ;o)

 

That said, if a CPU hack existed to consistently get 60mpg going 85mph.... imagine that?